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MPC Users Guide


Marine Prediction Center's Radiofacsimile Charts User's Guide



Marine Prediction Center Home Page; URL: http://www.mpc.ncep.noaa.gov/
Last Updated: September 8, 2000


Table of Contents

Introduction to Marine Prediction Center's (MPC) Radiofacsimile Program
500 MB Products
500 MB Analysis
6-Hour 500-mb Forecasts
24-Hour 500-mb Forecasts
36-Hour 500-mb Forecasts
48-Hour 500-mb Forecasts
96-Hour 500-mb Forecasts

Surface Products
Surface Analysis
48-Hour Surface Forecast
96-Hour Surface Forecast
Sea State Products
Sea State Analysis
48-Hour Wind/Wave Forecast
48-Hour and 96-Hour Wave Period Forecast

Regional Products
Regional Sea State Analysis
Regional 24-Hour Surface Forecast
Regional 24-Hour Wind/Wave Forecasts
Oceanographic Products
Marine Prediction Center's MFB Atlantic and Pacific Radiofacsimile Schedules
Description of Tropical Prediction Center's (TPC) Radiofacsimile Program
Summary




Marine Prediction Center Radiofacsimile Program
The National Weather Service (NWS) has the responsibility for issuing warnings
and forecasts to protect life and property in the maritime community. The area
of responsibility covers most of the North Atlantic and North Pacific N of 30N
with graphical products covering the marine areas S to 15N. Most of these
products are in graphical format and prepared by the NWS's National Centers For
Enviromental Prediction (NCEP) by its Marine Prediction Center (MPC). The Marine
Forecast Branch (MFB) a division of MPC at Camp Springs, MD, near Washington
D.C. is resposible for the issuance of various marine products. These products
are distributed by high-frequency (HF) Radiofacsimile broadcast via the US Coast
Guard Communications Centers at Boston, MA, and Pt Reyes, CA, for the North
Atlantic and North Pacific Oceans, respectively. Also, these products are
available on the internet on the Marine Prediction Center's Home Page.
High Seas Products
Vessels engaged in national and international trade routinely conduct
transoceanic voyages with fast turn around times between ports of call. Ships
require timely and accurate presentation of meteorological and oceanographic
information for a large geographical area to plan for safe and economical
operations. This information is most user friendly when presented in graphic
form. The MPC, which includes an operational service unit, the Marine Forecast
Branch (MFB), recognizes HF Radiofacsimile as the most widely used medium by
ships for receipt of graphically displayed environmental analyses and forecasts.

The following suite of products addresses the common needs and requirements of
professional mariners engaged in transoceanic crossings and offers the maritime
community complete and timely graphic products to support navigation safety and
operating efficiency. Three primary types of products are issued: upper air 500
millibar (mb) charts, surface pressure, and sea state charts. Additional charts
include sea surface temperatures (SST), tropical streamline and surface
analyses, and meteorological satellite imagery. Users whose specific or
specialized requirements for high seas information are not met by these general
safety-oriented products are referred to the private meteorological and
oceanographic sector for assistance.
Base Maps
There are two types of base maps. The larger scale ocean base map is a mercator
projection and has latitude and longitude marked in 10 degree increments. The
second type of base map is the regional which encompasses the west and east
coasts of the US covering subsections of the Atlantic and Pacific high seas
areas in polar stereographic projection.

NOTE about examples in the User's Guide :
In the descriptions of the marine radiofacsimile charts available, examples of
various charts are included within parenthese and are underlined, (48-Hr 12Z
Surface Forecast).



Upper Air 500-MB Products

The 500-mb charts are produced from a computer model of the atmosphere. These
products are automated unmodified computer outputs that depict height contours
above the earth's surface (geopotential heights) at 60 meter intervals. Wind
speeds of 30 knots and greater are shown with wind barb increments of 5 or 10
knots. Embedded within the 500-mb height field are short wave troughs, generally
50 degrees or less in longitude. These are drawn on the charts as bold dashed
lines. These short wave troughs will assist the mariner in locating surface low
pressure systems or developing lows on frontal waves. The 500-mb winds
approximate the speed of motion of surface extra-tropical lows (often about 1/3
to 1/2 of the 500-mb wind speed) and surface wind force (approximately 50
percent), particularly in the colder SW quadrant. The 5640 meter height contour
is highlighted since this height contour is widely used by the professional
mariner for general surface storm track direction and the southern extent of
Beaufort Force 7 (28-33 knot) or greater surface winds in the winter, and force
6 (22-27 knot) winds in summer. The 500-mb products are not intended to be used
alone. The mariner is strongly advised to examine other Radiofacsimile products
described in this User's Guide in order to derive a complete picture of weather
and sea state conditions.

500-mb Analyses
These analyses are generated twice a day at 00Z and 12Z (Atlantic 00Z 500-mb
[TIF|GIF|B/W GIF]). They depict synoptic scale flow patterns, location, and
amplitude of long and short waves. These synoptic scale features can be compared
with previous analyses to determine the movement and trends of the upper air
pattern. They can be used in conjunction with the surface analyses, sea state
analyses, and meteorological satellite imagery, which are valid at the same
synoptic time.

6-Hour 500-mb Forecasts
These forecasts come from the numerical model forecast 6 hours earlier and are
used when the current 500-mb analysis is not available.

24-Hour 500-mb Forecasts
These forecasts generated twice a day at 00Z and 12Z for the regional Atlantic
ocean are based on the latest numerical forecast model run. These products can
be used to compare changes in flow patterns from the latest 500-mb analyses to
follow the progression of short waves identified from the most recent 500-mb
analyses. The 500-mb 24-Hour Forecasts [TIF|GIF|B/W GIF] can be used in
conjunction with the Surface [TIF|GIF|B/W GIF] and Sea State [TIF|GIF|B/W GIF]
24-hour forecast products. Comparison or verification of previous 24-hour 500-mb
Forecasts with the most current 500-mb analysis can establish confidence in
subsequent forecasts.


36-Hour 500-mb Forecasts
These forecasts generated twice a day at 00Z and 12Z ([TIF|GIF|B/W GIF]) for the
Atlantic ocean are based on the latest numerical forecast model run. See 48-Hour
500-mb Forecast for further details.


48-Hour 500-mb Forecasts
These forecasts generated twice a day at 00Z and 12Z for each ocean are based on
the latest numerical forecast model run. These products can be used to compare
changes in flow patterns from the latest 500-mb analyses to follow the
progression of short waves identified from the most recent 500-mb analyses. The
500-mb 48-Hour Forecasts [TIF|GIF|B/W GIF] can be used in conjunction with the
Surface [TIF|GIF|B/W GIF] and Wind/Wave [TIF|GIF|B/W GIF] 48-hour forecast
products. Comparison or verification of previous 48-hour 500-mb Forecasts with
the most current 500-mb analysis can establish confidence in subsequent
forecasts.

96-Hour 500-mb Forecasts
These forecasts generated once a day at 00Z from the latest numerical model run.
These products can be used to compare changes in flow patterns from the latest
48-hour 500-mb forecast to follow the progression of short waves identified from
the most recent model guidance. The 500-mb 96-Hour Forecasts [TIF|GIF|B/W GIF]
can be used in conjunction with the 96-hour Surface Forecast [TIF|GIF|B/W GIF]
product.
 


Surface Products

These products include four surface analyses per day transmitted in two parts
and two 48-Hour Surface Forecasts daily. The computer workstation aided surface
analyses depict isobars, surface winds, frontal systems (occluded, stationary,
cold, and warm), low and high pressure center positions, and central pressure.
The 24 hour track history and 24 hour forecast position of each synoptic scale
system's position and central pressure are displayed on 48-hour surface
forecasts. Systems having or expected to have synoptic scale "Gale" or "Storm"
conditions are labeled in bold capital letters. Similarly systems expected to
develop "Gale" or "Storm" conditions in 36 hours have labels of "Developing
Gale" or "Developing Storm". Surface low pressure falls of 24 mb or greater
during a 24 hour period are denoted in large capital letters as "RAPIDLY
INTENSIFYING".
Standard abbreviations:
DSIPT - DISSIPATE
STNRY - STATIONARY
WKNG - WEAKENING
RPDLY - RAPIDLY
FRMG - FORMING
MOVG - MOVING
INLD - INLAND
DVLPG - DEVELOPING
COMB - COMBINED
DCRS - DECREASE
INCRS - INCREASE
INTSFY - INTENSIFY
Q-STNRY - QUASI-STNRY
For further information on terms or abbreviations used on surface products go to
the section Key terms & Symbols listed below.
For tropical cyclones, the alphanumeric description of the analyses or forecast
time are displayed in bold capital letters adjacent to the tropical cyclone's
position with the appropriate cyclone symbol.
TYPHOON or HURRICANE or TROPICAL STORM "NAME"
LATITUDE ___ LONGITUDE ___
MAX WINDS___ KT G (GUST) ___KT
MOV DIR ___ (DEGREES) AT __KT
A 24-hour tropical cyclone symbol forecast position will be depicted on all
surface analyses. Both 24-hour and 72-hour tropical cyclone positions will
appear on the 48-hour surface forecasts. Mariners are strongly advised to rely
on the latest warnings from the Tropical Prediction Center's (TPC) National
Hurricane Center (NHC) , which covers the Atlantic and the Eastern Pacific
Oceans east of 140W, and the Central Pacific Hurricane Warning Center (PHNL)
covering the Eastern and Central Pacific Ocean west of 140W to the international
dateline (180), and the Joint Typhoon Warning Center (JTWC), covering the
Western Pacific west of 180.
The surface forecasts produced by our marine meteorologists are derived by
comparing several U.S. and foreign government agencies forecast models. As a
result of the blending of these different model solutions, the surface forecasts
may not exactly coincide with the corresponding automated 500 mb forecasts.

Surface Analyses (Parts 1&2)
The surface analyses are generated four times per day (00Z, 06Z, 12Z, and 18Z)
for each ocean. The analyses consist of isobaric pressure analyses at 4 mb
contour interval spacing, labeled every 8 MB. The central pressure mb values of
low and high pressure systems are depicted in bold 3 or 4 digits and underlined
and placed adjacent to or under the "H" or "L". The surface analyses also
consist of abbreviated automated ship plots of wind direction (8 points on the
compass rose), wind speed (in knots) and present reported weather (using current
standard symbols). The product is issued in two parts, which overlap by some 10
degrees of longitude. Both parts will project the low or high pressure system's
forecast position by drawing an arrow to the 24-hour position labeled as an "X"
for lows and a circle with an "X" in the middle for highs with a bold two digit
millibar central pressure value underlined under or adjacent to the 24-hour
position label (e.g.,1050 mb high would be written as a 50 and a 960 mb low
would have 60). Significant weather systems have labels depicting whether the
system has "gale" or "storm" conditions as observed by ship and buoy
observations, Special Sensor Microwave Imagery (SSM/I), QuikSCAT, satellite, or
computer model guidance. If 36 hour forecast gale or storm conditions are
expected, the appropriate area has the label "developing gale" or "developing
storm". The surface analyses have been doubled in size and issued as a two part
product (00Z Pacific Part 1 [TIF|GIF|B/W GIF], Part 2 [TIF|GIF|B/W GIF]; 12Z
Atlantic Part 1 [TIF|GIF|B/W GIF] , Part 2 [TIF|GIF|B/W GIF]) to allow the
mariner to use the surface analyses as a work chart. The mariner can also have
the option to use the appropriate Parts 1 or 2 if operating only in that part of
the ocean which will impact the vessel. The mariner can also compare the ship's
current barometric pressure reading and Beaufort Wind Scale force conditions or
anemometer readout of winds observed at the vessel to determine the product's
validity. Mariners can then make their own inferences on how specific weather
systems will impact their vessels. Used in conjunction with a 500 mb analysis
(00Z Pacific [TIF|GIF|B/W GIF] , 12Z Atlantic [TIF|GIF|B/W GIF]), the 24 hour
forecast position of synoptic scale weather systems will aid in determining a
weather system's motion and intensity trends, thus extending the usefulness of
the product. The surface analyses will also be broadcast in a very timely
manner, less than 3 1/2 hours from the valid synoptic time. This product is an
important tool that can substantially aid in the independent decision making
process for crew safety, protection of the ship, prevention of cargo damage, and
maintaining schedules.

48-Hour Surface Forecasts
These surface forecast products generated twice each day at 00Z and 12Z for each
ocean based on the 00Z and 12Z AVN forecast model run outputs with additional
guidance from other government agencies such as the NAVYs Navy Operational
Global Atmospheric Prediction System (NOGAPS). Also, other foreign goverments
numerical model guidance is used such as the Canadian Regional Model. The use of
several numerical models allows adjustments to be made to the final forecast
product. The products show surface isobars every 4 mb with labeling of 2 digits
in increments of 8 mb. The central pressure millibar values of synoptic scale
lows and highs in bold 3 or 4 digits are underlined adjacent to or under the "L"
or "H". The 24-hour forecast position and future 72-hour forecast position of
lows and highs have vector arrows with an "X" for low centers and a "circle with
an X inside" by the head for high centers. An underlined bold two digit mb
central pressure value will be placed under or adjacent to the 24/72 hour
position label (e.g.,1050 mb high would be written as a 50 and a 960 mb low
would have 60). The 48-hour surface forecast depicts wind speeds in knots (wind
barbs in increments of 5 or 10 knots) for areas of wind in excess of 33 knots,
and frontal systems (occluded, warm, and cold). Significant systems have labels
depicting whether the system is expected to have "gale" or "storm" conditions.
If 72 hour forecast gale or storm conditions are expected, the appropriate area
has the label "developing gale" or "developing storm". The very timely issuance
of the 48-hour surface forecasts (12Z Atlantic 48-Hr Surface Forecast
[TIF|GIF|B/W GIF]), when used in conjunction with the 48-hour 500 mb and sea
state forecast products (Atlantic 48-Hr 12Z 500 mb [TIF|GIF|B/W GIF] and 48-Hr
12Z Wind/Wave[TIF|GIF|B/W GIF]), can help vessels make course and speed
adjustments to avoid the heaviest forecast wind and wave conditions or minimize
the ship's exposure to heavy weather. The tracking history and forecast
projection of highs and low from 24 hours through 72 hours will serve to extend
the time usage of the product, thus aiding a vessel's Master in the
determination of crew safety, minimizing ship or cargo damage, fuel economy, and
maintaining schedules.


96-Hour Surface Forecasts
These extended surface forecast products are generated once each day. The
product is based on the 00Z Medium Range Forecast (MRF) model for each ocean
with additional guidance from other government agencies such as the NAVYs Navy
Operational Global Atmospheric Prediction System (NOGAPS). Also, other foreign
goverments numerical model guidance is used such as the European Center for
Medium Range Weather Forecasts (ECMWF) and Canadian Regional Model. The use of
several numerical models allows adjustments to be made to the final forecast
product. The products show surface isobars every 4 mb with labeling of 2 digits
in increments of 8 mb. The central pressure millibar values of synoptic scale
lows and highs in bold 3 or 4 digits are underlined adjacent to or under the "L"
or "H". The 72-hour forecast position and future 120-hour forecast position of
lows and highs have vector arrows with an "X" for low centers and a "circle with
an X inside" by the head for high centers. An underlined bold two digit mb
central pressure value will be placed under or adjacent to the 72/120 hour
position label (e.g.,1030 mb high would be written as a 30 and a 980 mb low
would have 80). The 96-hour surface forecast depicts wind speeds in knots
greater than or equal to 34 kt (wind barbs in increments of 5 or 10 knots), and
frontal systems (occluded, warm, and cold). Significant systems have labels
depicting whether the system is expected to have "gale" or "storm" conditions.
If by 120 hours forecast gale or storm conditions are expected, the appropriate
area has the label "developing gale" or "developing storm". If a tropical system
such as a hurricane or typhoon is anticipated the 96-hour position will be
indicated as a "Low" with the pressure as "XXX" for an unknown pressure. The
72-hour position will correspond to the latest official forecast from the
responsible Typhoon Warning Center in the Pacific or the National Hurricane
Center in Miami, Florida. The 120-hour forecast position corresponds to Marine
forecasters estimated position. The issuance of the 96-hour surface forecasts
(Atlantic 96 Hr 00Z Surface Forecast [TIF|GIF|B/W GIF]), when used in
conjunction with the 96-hour 500 mb(Atlantic 96 Hr 00Z 500 mb [TIF|GIF|B/W
GIF]), can help vessels make course and speed adjustments to avoid the heaviest
forecast wind conditions or minimize the ship's exposure to heavy weather. The
tracking history and forecast projection of highs and lows from 72 hours through
120 hours will serve to extend the time usage of the product.


Sea State Products
One of the greatest hazards to a vessel's safety and seakeeping capability is
having to maneuver around and through changeable sea state conditions. Masters
have the awesome responsibility to make transoceanic crossings with crew safety
the highest in priority and then ensuring that the ship and its valuable cargo
arrive at destination ports safely while meeting tight schedules. The duration
of adverse or slowing seas must be minimized since turn around time in each port
is usually less than 24 hours. MPC issues one sea state analysis for both the
Atlantic and Pacific oceans on a daily basis. The MPC issues two 48-Hour
Wind/Wave Forecasts and one 96-Hour Wind/Wave Forecast each day. In addition two
48-Hour Period Forecasts and one 96-Hour Period Forecast are prepared each day.
During the winter cold season, the ice edge is depicted as a bold jagged line.
The contours for these products is in one meter intervals with a relative
maximum and minimum combined wave height values centrally displayed and inside a
box. Forecast of all wind speeds is also depicted. The sea state forecast when
viewed with the 48-hour surface forecasts will help vessels make course and
speed adjustments to avoid hazardous conditions and minimize exposure to slowing
conditions.
 

Sea State Analysis
This product is once a day per ocean at 00Z for the North Pacific and 12Z for
the North Atlantic (example, 12Z Atlantic [TIF|GIF|B/W GIF] and 00Z Pacific
Ocean [TIF|GIF|B/W GIF] ) with analysis of ship synoptic reports and automated
weather stations such as CMANs for sea state in "meters". The sea state analysis
is prepared for each ocean at the time of day when the greatest quantity of
observations are taken. The sea state analysis has solid 1 meter contour
intervals. Where appropriate, relative maxima and minima combined wave height
values (approximately 1/3 the height of the wind wave added to the height of the
swell wave) are centrally depicted and inside a box under or adjacent to the
wave height value. To produce the final analysis ships and buoys reporting
data along with the NCEP and Navy significant wave forecast models are used for
guidance in areas of sparse data and are used to verify model guidance. The sea
state analyses highlight where the most significant combined sea states prevail.
Primary swell direction arrows are also depicted. When viewed together with the
surface analyses, the user should have a complete picture of surface weather
conditions in a very timely manner, thus substantially aiding the mariner in
crew safety and the protection of property.



48-Hour Wind/Wave Forecast
These forecast products are generated twice daily. The forecasts valid at 00Z
and 12Z are based on the significant wave forecast model runs from NCEP and the
Navy. The combined sea heights are depicted in solid contours of one meter
increments with relative maxima or minima combined sea state values enclosed
inside a box under or adjacent to the area of interest. Also, the ice edge is
displayed as a bold jagged line during the winter months. These products will
provide a complete picture of forecast surface conditions when used in
conjunction with the 48-hour surface forecasts (00Z Pacific 48-Hour Wind/Wave
[TIF|GIF|B/W GIF] , 48-Hour Surface Forecast [TIF|GIF|B/W GIF]). The 48-hour
wind/wave forecasts highlight where the most significant combined sea heights
prevail. Also, forecast wind speed in knots are plotted on this chart.The
wind/wave forecasts products are issued in a timely manner and will
significantly aid in the independent decision-making process of heavy weather
avoidance, thus aiding vessels in minimizing the duration of encounter of
slowing or potentially damaging conditions.


48-Hour and 96-Hour Wave Period Forecast
Computer generated chart which is generated twice a day from the 00Z and 12Z
computer model runs. The 48-hour graphic is manually edited ( 00Z Pacific
48-Hour Wave Period Forecast [TIF|GIF| B/W GIF]) while the 96-hour graphic is
produced directly from computer output with no manual editing. The 96-hour
graphic is an experimental product. Depending on user feedback, the MPC may
implement the 96-hour product operationally on December 20, 2000. Customers can
send comments to:

National Weather Service
National Centers for Environmental Prediction
Marine Prediction Center
World Weather Building 5200 Auth Road, Room 410G
Camp Springs, M.D. 20746
Attn: David Feit, Branch Chief, Marine Forecast Branch, W/NP41

or
Email:David.Feit@noaa.gov

The forecast relies on guidance from the WaveWATCH III with forecasts for the
Atlantic and Pacific Oceans. The peak period identifies either the locally
generated `wind sea' (in cases with strong local winds) or the dominant wave
system (`swell') that is generated elsewhere. Note that the peak period field
shows discontinuities. These discontinuities can loosely be interpreted as swell
fronts, although in reality many swell systems overlap at most locations and
times. A swell front is the leading edge of wave periods with higher energy
which typically originates and moves away from a storm center. Arrows on the
forecast graphic point toward the prevailing swell direction.


Regional Products
Regional surface graphic products target coastal, offshore and high-seas users.
These products produced on polar stereographic map backgrounds encompass the
western Atlantic Ocean west of 50W and north of 30N, including the US east coast
and the central Florida coast. Also covered is the eastern North Pacific Ocean,
from the Baja peninsula, south to Cabo San Lucas, and north to the Gulf of
Alaska, including Prince William Sound as far west as 150W. The regional
products consist of the 00Z and 12Z sea state analysis and 24-hour forecasts of
the surface and wind/wave. The Marine Prediction Center issues the regional sea
state analysis and forecast products twice daily per ocean for 00Z and 12Z. The
sea state analysis shows ship observations with observed winds (knot) and sea
state in feet. The short range forecast products depict synoptic and mesoscale
features of surface low and high pressure systems and isobars with frontal
features, areas of reduced visibility, wind speeds, and significant wave height
as generated by the synoptic and mesoscale weather systems within 1000 miles of
the U.S. east and west coasts. The process of product preparation includes using
wind speeds derived from Special Sensor Microwave Imagery (SSM/I), and QuikSCAT
received from polar orbiting satellite from oceanic areas. This high state of
the art technology of data input represents a significant enhancement in
analyzing wind conditions in the marine environment. SSM/I and QuikSCAT is
especially noteworthy in data sparse areas where there are no ship or buoy
reports. SSM/I and QuikSCAT aids in short range prediction of the 24-hour
forecast products by enabling marine meteorologists to compare initial data from
forecast model output and making the necessary adjustments to the near term
forecast solutions.

Regional Sea State Analysis
This product is issued every three hours and is broadcast on the radiofacsimile
program twice a day per ocean at 00Z and 12Z (example, 12Z Atlantic [TIF|GIF|B/W
GIF] with analysis of ship synoptic reports and automated weather stations such
as CMANs for sea state in "feet"and observed windspeed (knot). The sea state
analysis has solid three foot contour intervals. Where appropriate, relative
maxima and minima combined wave height values (approximately 1/3 the height of
the wind wave added to the height of the swell wave) are centrally depicted and
inside a box with the maximum or minimum values. To produce the final analysis
ships and buoys reporting data along with the NCEP and Navy significant wave
forecast models are used for guidance in areas of sparse data and are used to
verify model guidance. The sea state analyses highlight where the most
significant combined sea states prevail. When viewed together with the surface
analyses, the user will have a complete picture of surface weather conditions in
a very timely manner, thus substantially aiding the mariner in crew safety and
the protection of property.


Regional 24-Hour Surface Forecast
This product is a surface forecast chart featuring low and high pressure center
positions with bold 3-and 4-digit central pressure values underlined under or
adjacent to the "L" or "H" (00Z Atlantic 24-Hour Surface Forecast [TIF|GIF|B/W
GIF]). An arrow points to the 48-hour forecast position of lows and highs with
an "X" for low centers and a "circle with an X inside" by the head for high
centers. Significant systems have labels depicting whether the system is
expected to have gale or storm conditions. If 24 hour forecast "gale" or "storm"
conditions are expected the system the system is labelled with the appropriate
warning. If "gale" or "storm" conditions are expected by 48 hours the
appropriate area has the label "developing gale" or "developing storm". Also
displayed on this surface forecast chart are frontal systems (occluded, warm,
and cold) and when appropriate, associated areas of fog, signifying areas of
potential restriction to visibility. The frontal systems themselves imply
regions of visibility-reducing precipitation, which for the sake of clarity and
brevity are not depicted. Isobars (lines of equal surface pressure) are depicted
in increments of 4 mb except 8 mb for deep systems (i.e., 960 mb). The 1000 mb
contour will be dashed to separate 4 mb from 8 mb contour spacing.


Regional 24-Hour Wind/Wave Forecast
This forecast product depicts 24-hour forecasts (00Z Atlantic 24-Hour Wind/Wave
Forecast [TIF|GIF|B/W GIF]) of wind (increments of 5 knots) and significant wave
heights (isopleths of combined sea and swell in 3 foot intervals). During
appropriate weather conditions such as "North Wall" episodes occurring along the
northern wall of the Gulf Stream in the western Atlantic, substantially higher
wind/wave height values are highlighted. Arrows will point to a superimposed
hatched area of the Gulf Stream. The "North Wall" event is normally confined to
the adjacent areas of the northern edge of the Gulf Stream. Another item that
may be highlighted on the forecast is "Swell fronts" which may originate from
tropical systems. These "Swell fronts" can be hazardous conditions to marine
operations and those in coastal areas. A scalloped line is used to depict the
front and is labelled appropriately such as "SWELL FRONT FROM HURRICANE DEBBY"
Arrows will be from the text to the leading edge of the "Swell front" Forecast
guidance to prepare this product are provided by wave height and wave period
models from NCEP and the US Navy. The wave height values are depicted by solid
contours in increments of three feet. Superstructure icing, displayed by a half
moon with one or two lines crossing through the center, will depend on the
forecast for light or heavy accumulation.


Oceanographic Products

Oceanographic Operational Products-Sea Surface Temperature (SST)
There are two ocean charts available on the Pacific Radiofacsimile program. Each
of the charts is updated once a day with automated Sea Surface Temperature
(SST) analyses derived from (IR) Infrared Satellite. The northern chart includes
the nearshore waters of Washington and Oregon as well as the coastal waters of
Vancouver Island and Queen Charlotte Sound in Canada; [TIF|GIF|B/W GIF] SST
Analysis (40N-53N, EAST OF 136W). The southern chart includes all of California,
the Baja peninsula, and most of the coastal waters of western Mexico, south to
near Puerto Vallarta; [TIF|GIF|B/W GIF] SST Analysis (23N-42N, EAST OF 136W).
NOTE: Like weather charts, oceanographic charts depict operational data that are
part of the total data set of the National Oceanic and Atmospheric
Administration. The charts reflect a basic analysis of the data to support safe
and efficient operations in the marine environment. If these products do not
meet their specific operational requirements, users should consult the private
meteorological and oceanographic community for further assistance.

Key terms and Symbols

FRONTS

Cold front
-The leading edge of a relatively colder airmass which separates two air
masses in which the gradients of temperature and moisture are maximized.
In the northern hemisphere winds ahead of the front will be southwest
and shift into the northwest with frontal passage.

Frontogenesis
-The formation of a front occurs when two adjacent air masses with
different densities and temperatures meet and strengthen the
discontinuity between the air masses. It occurs most frequently over
continental land areas such as over the Eastern US when the air mass
moves out over the ocean. It is the opposite of frontolysis.

Frontolysis
-The weakening or dissipation of a front occurs when two adjacent air
masses lose contrasting properties such as the density and temperature.
It is the opposite of frontogenesis.

Occluded front
- The union of two fronts, formed as a cold front overtakes a warm front
or quasi-stationary front refers to a cold front occlusion. When a warm
front overtakes a cold front or quasi-stationary front the process is
termed a warm front occlusion. These processes lead to the dissipation
of the front in which there is no gradient in temperature and moisture.

Ridge
- an elongated area of relatively high pressure that is typically
associated with a anticyclonic wind shift.

Stationary front
- A front that has not moved appreciably from its previous analyzed
position.

Trough
- [Trof], an elongated area of relatively low pressure that is typically
associated with a cyclonic wind shift.

Warm front
- The leading edge of a relatively warmer surface air mass which
separates two distinctly different air masses. The gradients of
temperature and moisture are maximized in the frontal zone. Ahead of a
typical warm front in the northern hemisphere, winds are from the
southeast and behind the front winds will shift to the southwest.

LOW & HIGH PRESSURE SYSTEMS AND MISCELLANEOUS KEY TERMINOLOGY USED

Low pressure with a number such as 99 means 999 mb and with 03 means
1003 mb. High pressure with a number such as 25 means 1025 mb.

Extratropical low
- A low pressure center which refers to a migratory frontal cyclone of
middle and higher latitudes. Tropical cyclones occasionally evolve into
extratropical lows losing tropical characteristics and become associated
with frontal discontinuity.

Low pressure
- An area of low pressure identified with counterclockwise circulation
in the northern hemisphere and clockwise in the southern hemisphere.
Also, defined as a cyclone.

High pressure
- An area of higher pressure identified with a clockwise circulation in
the northern hemisphere and a counterclockwise circulation in the
southern hemisphere. Also, defined as an anticyclone.

New
- The term "NEW" may be used in lieu of a forecast track position of a
high or low pressure center when the center is expected to form by a
specific time. For example, a surface analysis may depict a 24-hour
position of a new low pressure center with an "X" at the 24-hour
position followed by the term"NEW", the date and time in UTC which
indicates the low is expected to form by 24 hours.

Rapidly intensifying
- Indicates an expected rapid intensification of a cyclone with surface
pressure expected to fall by at least 24 millibar (mb) within 24 hours.

Station plot
Click for information on coding used with the surface preliminary
analysis or for a list of "present weather" symbols.

Station ID = KPZH
temperature (F or C) = 70 = 70 degree FStation Pressure (mb) = 048
= 1004.8 mb
present weather = = thunderstorm3 hour pressure tendency = -7 \ =
-0.7 mb pressure decrease with steady pressure f
dew point temperature (F or C) = 68= 68 degree Fwave height (ft or
m) = 11 ft
wind speed & direction = SSW 25 kt
sky cover = overcast Sea Surface Temperature (F or C) = 75 = 75
degrees F


Squall
- A sudden wind increase characterized by a duration of minutes and
followed by a sudden decrease in winds.

Windspeed & Direction

FOG

Fog
- Over the marine environment the term fog refers to visibility
greater than or equal to 1/2 NM and less than 3 NM. Fog is the visible
aggregate of minute water droplets suspended in the atmosphere near
the surface.

Dense fog
-Over the marine environment the term dense fog refers to visibility
less than 1/2 NM. Fog is the visible aggregate of minute water
droplets suspended in the atmosphere near the surface. Usually dense
fog occurs when air that is lying over a warmer surface such as the
Gulf Stream is advected across a colder water surface and the lower
layer of the airmass is cooled below its dew point.

Sea fog
- Common advection fog caused by transport of moist air over a cold
body of water.
FREEZING SPRAY

Freezing spray
- Spray in which supercooled water droplets freeze upon contact with
exposed objects below the freezing point of water. It usually develops
in areas with winds of at least 25 knots.
Categories of Freezing Spray/IcingLightModerateHeavy
Less than 0.7 cm/hr 0.7 cm/hr to less than or equal to 2.0
cm/hrGreater than 2.0 cm/hr
Less than 0.3 ins/hr0.3 ins/hr to less than or equal to 0.8
ins/hrGreater than 0.8 ins/hr

CONVENTIONS USED WITH WARNINGS FOR EXTRATROPICAL SYSTEMS
Extratropical Systems
Complex gale/storm
-An area in which gale/storm force winds are forecast or are
occurring, but in which more than one center is the generating these
winds.

Developing gale
-Refers to an extratropical low or an area in which gale force winds
of 34 knots (39 mph) to 47 knots (54 mph) are "expected" by a certain
time period. On surface analysis charts a developing gale indicates
gale force winds within the next 36 hours. When the term developing
gale is used on the 48 hour surface forecast and 96 hour surface
forecast charts, gale force winds are expected to develop by 72 hours
and 120 hours, respectively.

Developing storm
-Refers to an extratropical low or an area in which storm force winds
of 48 knots (55 mph) or greater are "expected" by a certain time
period. On surface analysis charts a developing storm indicates storm
force winds forecast within the next 36 hours. When the term
developing storm is used on the 48 hour surface and 96 hour surface
charts, storm force winds are expected to develop by 72 hours and 120
hours, respectively.

Gale
- Refers to an extratropical low or an area of sustained surface winds
(one minute) of 34 knots (39 mph) to 47 knots (54 mph).

Storm
- Refers to a extratropical low or a area of sustained winds (one
minute) in excess of 48 knots (55 mph).

Small Craft Advisory
- Refers to areas within the coastal waters with sustained winds (one
minute) of 18 knots (21 mph) to 33 knots (38 mph).

CONVENTIONS USED WITH WARNINGS FOR TROPICAL SYSTEMS

Tropical Systems

Hurricane
- A tropical cyclone with closed contours, a strong and very
pronounced circulation, and one minute maximum sustained surface winds
64 knots (74 mph) or greater. A system is called a hurricane over the
North Atlantic, Gulf of Mexico, North Pacific E of the dateline, and
the South Pacific E of 160E.

Tropical cyclone
- A non-frontal, warm-core, low pressure system of synoptic scale,
developing over tropical or subtropical waters with definite organized
convection (thunderstorms) and a well defined surface wind
circulation.

Tropical depression
- A tropical cyclone with one or more closed isobars and a one minute
max sustained surface wind of less than 34 knots (39 mph).

Tropical storm
- A tropical cyclone with closed isobars and a one minute max
sustained surface wind of 34 knots (39 mph) to 63 knots (73 mph).

Typhoon
- Same as a hurricane with exception of geographical area. A tropical
cyclone with closed contours, a strong and very pronounced
circulation, and one minute maximum sustained surface winds of 64
knots (74 mph) or greater. A system is defined as a typhoon over the
North Pacific W of the dateline.

SEAS

Combined seas
-The combination of both wind waves and swell which is generally
referred to as "seas".

Primary swell direction
- Prevailing direction of swell propagation.

Significant wave height
- The average height (trough to crest) of the 1/3rd highest waves. An
experienced observer will most frequently report the highest 1/3rd of
the waves observed.

Swell
- Wind waves that have moved out of their fetch or wind generation
area. Waves generated by swell exhibit a regular and longer period
than wind waves.


MISCELLANEOUS TERMINOLOGY

High Seas
- That portion of the Atlantic and Pacific oceans which is the area of
responsibility of the Marine Prediction Center that extends from 20 to
40 nm off the Western and Eastern US coasts and extends to 35W in the
Atlantic ocean and to 160E in the Pacific Ocean. The area includes
both the coastal and offshore waters.

Offshore waters
- That portion of oceans, gulfs, and seas beyond coastal waters
extending to a specified distance from the coastline, to a specified
depth contour, or covering an area defined by a specific latitude and
longitude points.


Marine Prediction Center's MFB Radiofacsimile Schedule
The Atlantic and Pacific Radiofacsimile schedules list product times of
transmission, request for comments on products, and product notice bulletins.
During periods of lost or bad data, transmission problems, etc., information on
the nature of the problem will be substituted for the scheduled product or
substituted in the beginning of each broadcast cycle in place of the test
pattern, as time and resources permit. If there are available time slots with
the U.S. Coast Guard transmission schedule and lesser schedules priorities, and
the U.S. Coast Guard agrees, every attempt will be made to rebroadcast the
product. Most likely, the retransmission will occur at the end of the scheduled
broadcast cycle.


Tropical Prediction Center's Radiofacsimile Program
The counterpart to the Marine Prediction Center is the Tropical Prediction
Center's Tropical Analysis and Forecast Unit which has responsibility for marine
forecasts in the tropics and subtropics for the area S of 30N to the equator and
E of 140W in the Pacific and S of 30N to the equator W of 35W in the Atlantic.
The TAFB Radiofacsimile Program consists of two product suites: surface analysis
products and marine forecast products. A east Pacific Wind/Seas Analysis
(example 18Z [TIF|GIF]) is prepared by TAFB and is broadcast with forecast
products from MPC through transmitters of the U.S. Coast Guard at Point Reyes,
California with charts for 12Z and 18Z . The graphic includes winds in knots and
seas state values in feet. The chart also includes Tropical systems with the
latest analyzed position and wind speed. Refer to the latest MPC Pacific
Radiofacsimile schedule for transmission times and broadcast frequencies of this
product.
For further information on the Tropical Prediction Center's TAFB Radiofacsimile
program and its latest schedule please E-mail your comments to the Tropical
Prediction Center. Additional information can be obtained by phone:
(305)-229-4430, fax: (305)-553-1264, or writing to:
Chief, TAFB
Tropical Prediction Center
11691 SW 17th St.
Miami, FL 33165-2149

Summary


In consultation with its users, MPC has designed a timely product suite of
graphics and high seas marine warnings and forecasts. When displayed together
and organized the charts provide the mariner with a complete meteorological and
oceanographic picture. Prudent decision making dictates the mariner use all
available information from as many sources as possible.
The MPC's Marine Radiofacsimile Charts and Warning Forecasts program is designed
to assist mariners in making decisions regarding the protection of the crew from
injury, prevention of ship and cargo damage, fuel economy, and meeting fixed
schedules, as well as serving the commercial fishing and recreational
communities. The product suite is based on user feedback and input, and is
always subject to review and revision. We strongly encourage input from the
marine user community.


For additional information contact:

National Weather Service
National Centers for Environmental Prediction
Marine Prediction Center
World Weather Building 5200 Auth Road, Room 410 Camp Springs, M.D. 20746
Attn: David Feit, W/NP41
Phone: 301-763-8441
Fax: 301-763-8592, 301-763-8085
Email:David.Feit@noaa.gov
Marine Prediction Center Home Page; URL: http://www.mpc.ncep.noaa.gov/

Last modified on Wednesday, October 18, 2000

 

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Webmaster- Rob Dubin                             copyright 2003-2006   Rob  Dubin               Page Last updated 09/02/2006