TAFB/Marine Product Descriptions

Tropical Weather Discussion

Purpose

The Tropical Weather Discussion describes major synoptic weather features and significant areas of disturbed weather in the tropics. The product is intended to provide current weather information for those who need to know the current state of the atmosphere and expected trends to assist them in their decision making. The product gives significant weather features, areas of disturbed weather, expected trends, the meteorological reasoning behind the forecast, model performance, and in some cases a degree of confidence.

Content

The Tropical Weather Discussion is a narrative explaining the current weather conditions across the tropics and the expected short-term changes. The product is divided into four different sections as outlined below:

1. SPECIAL FEATURES (event-driven)
   The special features section includes descriptions of hurricanes, tropical storms, tropical depressions, subtropical cyclones, and any other feature of significance that may develop into a tropical or subtropical cyclone. For active tropical cyclones, this section provides the latest advisory data on the system. Associated middle and upper level interactions as well as significant clouds and convection are discussed with each system. This section is omitted if none of these features is present.
2. TROPICAL WAVES (event-driven)
   This section provides a description of the strength, position, and movement of all tropical waves analyzed on the surface analysis, from east to west. A brief reason for a wave's position is usually given, citing surface observations, upper air time sections, satellite imagery, etc. The associated convection is discussed with each tropical wave as well as any potential impacts to landmasses or marine interests. This section is omitted if there are no tropical waves present.


3. ITCZ
   In this section, the Intertropical Convergence Zone (ITCZ) is depicted by coordinates from east to west with an outline of all associated convection referenced to the axis, if possible. The ITCZ is depicted based on the following definition: "a zonally elongated axis of surface wind confluence in the tropics, due to confluence of northeasterly and southeasterly trade winds, and/or confluence at the poleward extent of cross-equatorial flow into a near-equatorial 'heat trough' or 'monsoon trough.'"


4. DISCUSSION
   The discussion section makes reference to middle and upper level features and provides connection to how these features are interacting with or influencing surface features. Convection is outlined with the features as warranted. This section will also provide short-term (up to 48 hours) trends and forecasts of features, especially if they are forecast to strengthen and/or affect landmasses. A discussion of model guidance may also be included. In general, this section is regionalized according to the current weather pattern (i.e. Gulf of Mexico, Caribbean, Western Atlantic, etc.)

Coverage and intensity for convective and non-convective weather is defined as follows:

COVERAGE FOR CONVECTIVE and NON-CONVECTIVE WEATHER:

COVERAGE FOR SIGNIFICANT CLOUDS:

INTENSITY OF CONVECTION (based on cloud top temperatures):

Coverage

The National Hurricane Center issues two Tropical Weather Discussions, as shown below:

1. Atlantic
   From the equator to 32°N west of the prime meridian including the Caribbean Sea, Gulf of Mexico, and adjacent land areas. These areas include the southeast United States [especially Florida], Mexico, Central America, northern South America, and western Africa
2. East Pacific
   From the equator to 32°N east of 140°W including coastal areas of Mexico, and Central and South America.

Issuance/Transmission

	WMO	NWWS
Atlantic	AXNT20 KNHC	MIATWDAT
East Pacific	AXPZ20 KNHC	MIATWDEP

High Seas Forecasts

Purpose

The world's oceans and seas are divided up into 16 separate regions known as "METAREAS" with different nations having responsibility for providing high seas marine forecasts for those waters. These high seas forecasts are used mainly by large transoceanic vessels but can also be used by smaller vessels or those on shorter voyages. The U.S. National Weather Service (through the National Hurricane Center, the Ocean Prediction Center, and the Honolulu Weather Forecast Office) has the responsibility to provide high seas marine forecasts for METAREAS IV, XII, and XVI, which cover most of the North Atlantic Ocean, North Pacific Ocean, and Southeast Pacific Ocean.

Content

The National Hurricane Center issues three High Seas Forecasts for parts of METAREAS IV and XII and all of METAREA XVI. Each product is updated every 6 hours and includes a description of winds and waves for the current time (a nowcast) and a 24- and 48- hour forecast of the winds and waves, using a 20 knot threshold for the wind and an 8 feet threshold for the seas. Positions and intensities are also given for tropical cyclones out to the 120-hour forecast. Intermediate forecast times are given for rapidly changing weather events. The High Seas products also include updated descriptions of convection, particularly along the ITCZ. The products include marine warnings for gale, storm, hurricane force winds, and tropical cyclone-related conditions and can also include information on reduced visibility and other marine hazards.

Coverage

1. Atlantic Ocean (from 7°N to 31°N west of 35°W, including the Caribbean Sea and the Gulf of Mexico)
2. Northeast Pacific Ocean (from the equator to 30°N east of 140°W)
3. Southeast Pacific Ocean (from the equator to 18.5°S east of 120°W)

Issuance/Transmission

High seas products are transmitted under World Meteorological Organization (WMO) and NOAA Weather Wire Service (NWWS) headers as shown in the following table (alternate headers are for high seas products issued by the Ocean Prediction Center, which append the forecasts of the National Hurricane Center):

High seas products are issued on a regular six hourly schedule as shown below:

Alternate headers for the Atlantic and Northeast Pacific Forecasts are where TAFB forecasts are appended to High Seas Forecasts of the Ocean Prediction Center. In addition, Atlantic high seas products are transmitted by radiofax.

Offshore Waters Forecasts

Purpose

The Offshore Waters Forecast provides forecast and warning information to mariners who travel the oceanic waters adjacent to the U.S. and its territorial coastal waters. This forecast serves customers who operate from the coastal waters to several hundred nautical miles from shore with 10 different products issued by the National Hurricane Center, the Ocean Prediction Center, the Honolulu Weather Forecast Office, the Anchorage Weather Forecast Office, and the Juneau Weather Forecast Office.

Content

The Offshore Waters Forecast includes a synopsis which describes significant surface weather features that may cause significant winds and seas over the forecast area during the forecast period. The synopsis identifies major weather systems and the strength, trend, and movement of each. The most detail is focused in the first 48 hours of the forecast. The synopsis also includes tropical cyclone forecast positions out to 120 hours.

The offshore waters product provides a forecast for winds and seas over the affected area for roughly the next 5 days. The forecast also includes significant weather which would pose a hazard to navigation, such as precipitation or restrictions to visibility. Warnings are issued when conditions are expected to meet the specific warning criteria during the first two periods of the forecast. Thereafter, a headline is used which shows that the conditions are expected to occur at some time after the first two periods.

Coverage

The National Hurricane Center issues two separate Offshore Waters Forecasts, as shown below:

Gulf of Mexico offshore waters:

1. Northwest Gulf (north of 25°N west of 90°W)
2. Southwest Gulf (south of 25°N west of 90°W)
3. Middle Gulf (between 85°W and 90°W)
4. Eastern Gulf (between 81°W and 85°W)

Southwest and Tropical North Atlantic and Caribbean offshore waters:

1. Northwest Caribbean (north of 15°N west of 75°W)
2. Southwest Caribbean (south of 15°N west of 75°W)
3. Eastern Caribbean (east of 75°W to Leeward and Windward Islands)
4. Tropical North Atlantic (from 7°N to 22°N between 55°W and 65°W)
5. Southwest North Atlantic (south of 31°N west of 65°W including the Bahamas)

Issuance/Transmission

Offshore waters products are transmitted under World Meteorological Organization (WMO) and NOAA Weather Wire Services (NWWS) headers as shown in the following table:

Offshore waters products are issued on a regular six hourly schedule as shown below:

Marine Weather Discussion

Purpose

The Marine Weather Discussion is a semi-technical product, analogous to the Area Forecast Discussion (AFD) issued by the local National Weather Service Forecast Offices, primarily used as a means to explain the scientific rationale behind the Offshore Waters Forecast and to summarize the warnings in effect. The Marine Weather Discussion is used to convey forecast and warning information to federal agencies, weather-sensitive officials, and the media. Part of this goal is to enhance coordination with the coastal Weather Forecast Offices.

Content

The Marine Weather Discussion describes synoptic and mesoscale features expected to affect areas in and adjacent to the offshore waters of the Gulf of Mexico, Caribbean Sea, and Southwest and Tropical North Atlantic Ocean. The narrative describes weather, wind speed, and seas with primary focus on the next 48 hours. The product emphasizes timing and issuance of warnings, includes future trends of wind and sea conditions, discusses the effects of currents such as the Gulf Stream on winds and seas, and addresses how the latest computer model guidance is handling features of significance to the mariner.

Coverage

The National Hurricane Center issues one Marine Weather Discussion to convey forecast reasoning over both its offshore forecast areas. This area includes the Gulf of Mexico, the Caribbean Sea, the Tropical North Atlantic, and the Southwest North Atlantic Ocean south of 31°N west of 55°W. The area between 55°W and 65°W is not specifically covered by the Offshore Waters Forecast products, but conditions in this area are discussed since they often affect the offshore waters in the future.

Issuance/Transmission

The Marine Weather Discussion is transmitted under World Meteorological Organization (WMO) and NOAA Weather Wire Services (NWWS) headers as shown below:

In general, the Marine Weather Discussion is issued twice a day (with updates as needed) shortly before the issuance of the scheduled Offshore Waters Forecast products. Forecasters will issue a brief discussion to provide information of an impending offshore forecast update. The scheduled transmission times are shown below:

Pan-American Temperature and Precipitation Table

Purpose

The Pan-American Temperature and Precipitation Table is a collection of temperature and precipitation data and present weather for selected cities in Mexico, Central and South America, and the Caribbean area. It provides general weather conditions two times per day for general public use domestically and internationally.

Content

This product provides general weather conditions, high and low temperatures in degrees Fahrenheit (°F) and degrees Celsius (°C), and measured precipitation in the previous 6, 12, or 24 hours, as indicated, for selected cities in Mexico, Central and South America, and the Caribbean area. The morning product contains the low temperature for the current day and the high temperature for the previous day. The evening product contains the low and high temperature for the current day.

Coverage

The Pan-American Temperature and Precipitation Table includes the following stations (as shown in the map above):

Issuance/Transmission

The Pan-American Temperature and Precipitation Table is transmitted under World Meteorological Organization (WMO) and NOAA Weather Wire Services (NWWS) headers as shown below:

	Valid Time	Issuance Time
Morning MIATPTPAN	700 AM EST (800 AM EDT)	by 950 AM EST (1050 AM EDT)
Evening MIATPTPAN	700 PM EST (800 PM EDT)	by 950 PM EST (1050 PM EDT)

Satellite Rainfall Estimates (Woodley-Griffith technique)

Purpose

Satellite rainfall estimates are provided for tropical cyclones or other significant convective systems (mainly in the tropics) when these systems threaten land. The product is issued when convection systems are affecting the WMO RA-IV area. The product is also issued when system affect the west coast of Mexico. These estimates are based on geostationary infrared satellite imagery using a method called the Woodley-Griffith Technique.

Content

The satellite rainfall estimate product provides an estimate of the maximum rainfall based on the last four geostationary satellite images six hours apart (24 hours), as well as the estimated maximum rainfall based on the latest geostationary satellite image. The product also provides a rainfall distribution within 4° (240 nautical miles) to the left and right of the observed system motion in 1° (60 nautical miles) increments.

Coverage

One of three satellite rainfall estimate products is issued for each convective system affecting or expected to affect land based on the system.s initial location:

1. Eastern Caribbean (areas between 40°W and 67°W)
2. Central Caribbean (areas between 67°W and 80°W)
3. Western Caribbean / Mexico (areas between 80°W and 120°W)

Issuance/Transmission

The Satellite Tropical Disturbance Rainfall Estimate product is transmitted under World Meteorological Organization (WMO) and NOAA Weather Wire Services (NWWS) headers as shown below:

The product is issued four times a day as needed near the synoptic times of 0000, 0600, 1200, and 1800 UTC. The exact issuance time is based on the time of the last satellite image used.

Tropical Surface Analysis / NWS Unified Surface Analysis

Purpose

The Tropical Surface Analysis is created every six hours to depict the current state of atmosphere, specifically the sea level pressure field and any relevant synoptic surface features. The Tropical Surface Analysis is attached to surface analyses over North America, the North Atlantic Ocean, the North Pacific Ocean, and the Western Pacific Ocean to create the National Weather Service Unified Surface Analysis.

Content

The Tropical Surface Analysis and NWS Unified Surface Analysis depict the sea level pressure field by showing lines of equal pressure, usually in increments of four millibars (mb) but often in increments of two millibars where the pressure gradient is weaker (especially in the tropics). The analysis also depicts important surface features that affect the weather, including areas of high and low pressure, frontal systems (cold, warm, stationary, and occluded), troughs, tropical cyclones, tropical waves, the Intertropical Convergence Zone (ITCZ), drylines, and squall lines.

Coverage

The Tropical Surface Analysis is created by the National Hurricane Center and covers the area approximately from 30°N to 20°S between 0° and 140°W. This area includes the tropical and subtropical areas of the Atlantic and East Pacific Oceans, Mexico, Florida, the Caribbean, South America, and West Africa. For radiofax purposes, the analysis is split into three different areas:

1. Atlantic (East Half from 5°S to 50°N between 0° and 70°W)
2. Atlantic (West Half from 5°S to 50°N between 55°W and 125°W)
3. Eastern Pacific (from 20°S to 40°N between 70°W and 150°W)

The NWS Unified Surface Analysis is created by merging the separate surface analysis produced by the National Hurricane Center, the Hydrometeorological Prediction Center, the Ocean Prediction Center, and the Honolulu Weather Forecast Office. The total area spans from the equator northward nearly to the North Pole, from 20°E westward to 130°W. This covers the area from Europe and Central Africa westward across North and South America to East Asia.

Issuance/Transmission

The Tropical Surface Analysis is transmitted by radiofax via New Orleans, Pt. Reyes, and Honolulu according to the following table:

The analyses are also updated on the NHC webpage by 0300, 0900, 1500, and 2100 UTC for the 0000, 0600, 1200, and 1800 UTC surface analyses, respectively.

Sea State Analysis

Purpose

Content

The significant wave height is contoured at intervals of three feet, with additional contours added if necessary in areas of little spatial variation. The significant wave height is defined as the average height of the highest 1/3 of the waves (individual waves may be more than twice the significant wave height). Maximum and minimum significant wave height values are indicated as necessary. Arrows are also depicted showing the primary swell direction at specific points.

Coverage

The National Hurricane Center produces two separate sea state analyses twice a day:

1. Atlantic (from the equator to 31°N between 35°W and 100°W, including the Pacific east of 100°W)
2. East Pacific (from 20°S to 30°N east of 145°W)

Issuance/Transmission

	New Orleans, LA		Pt. Reyes, CA		Honolulu, HI
Valid Time (UTC)	Transmission Time (UTC)	Filename	Transmission Time (UTC)	Filename	Transmission Time (UTC)	Filename
0000	0215	PJEA88.TIF	0205	PKFA88.TIF	0240	PKFA88.TIF
1200	1415	PJEA90.TIF	1425	PKFA89.TIF	1440	PKFA89.TIF
latest		PJEA11.TIF		PKFA10.TIF		PKFA10.TIF

Tropical Cyclone Danger Graphic (Mariner's 1-2-3 Rule)

Purpose

The tropical cyclone danger graphic is intended to depict the forecast track and corresponding area of avoidance for all active tropical cyclones and to depict areas for which tropical cyclone formation is possible within the next 36 hours over the Atlantic and East Pacific waters between May 15 and November 30.

Content

The 3-day forecast track of each active tropical cyclone is depicted along with a shaded "danger" region, or area of avoidance. The danger area is determined by adding 100, 200, and 300 nautical miles to the tropical storm force radii (34 knots) at the 24-, 48-, and 72-hour forecast positions, respectively (hence the Mariner's 1-2-3 rule). Users operating in the vicinity of these systems are advised to continually monitor the latest forecasts and advisories issued by the National Hurricane Center. Areas are also shaded for systems in which NHC forecasters believe there is an adequate chance of tropical cyclone formation within the next 48 hours.

Coverage

The National Hurricane Center produces tropical cyclone danger graphics covering the following areas:

1. Atlantic (from the equator to 60°N between 0° and 100°W, including the Pacific east of 100°W)
2. East and Central Pacific (from the equator to 40°N between 80°W and 175°W, including the Gulf of Mexico and Western Caribbean)

Issuance/Transmission

The tropical cyclone danger graphics are transmitted by radiofax via Boston, New Orleans, and Pt. Reyes according to the following table:

High Wind and Associated Seas

Purpose

The high wind and associated seas graphic is produced by the National Hurricane Center to depict areas of high winds and related seas over the Atlantic and East Pacific waters between December 1 and May 14 (outside of hurricane season).

Content

Areas depicted on the high wind and seas graphic are extracted from the high seas forecasts produced by the National Hurricane Center, the Ocean Prediction Center, and the Honolulu Weather Forecast Office. South of 30°N, areas are depicted for winds higher than 25 knots with the corresponding seas noted. North of 30°N, areas are depicted for winds of gale force (34 knots) or higher with the corresponding seas noted. Ranges in which the 25/34 knot thresholds are the upper limit (i.e. 25-35 knots) are included on the graphic.

Coverage

The National Hurricane Center produces high wind and seas charts covering the following areas:

1. Atlantic (from the equator to 40°N between 35°W and 100°W, including the Pacific east of 100°W)
2. East Pacific (from the equator to 40°N between 80°W and 150°W)

Issuance/Transmission

The high wind and associated seas graphics are transmitted by radiofax via Boston, New Orleans, and Pt. Reyes according to the following table:

Wind/Wave Forecasts

Purpose

Wind/wave forecasts are produced to depict the 24-, 48-, and 72-hour forecasts of surface features, surface wind speed and direction, and significant wave heights over the tropical and subtropical Atlantic and East Pacific waters.

Content

The wind/wave forecasts include relevant surface features, including areas of high and low pressure, frontal systems (cold, warm, stationary, and occluded), troughs, ridges, tropical waves, and tropical cyclones. Wind barbs indicate the forecast wind speed and direction at specific points where long barbs indicate 10 knots and short barbs indicate 5 knots. The significant wave height is contoured at intervals of three feet, with additional contours added if necessary in areas of little spatial variation. The significant wave height is defined as the average height of the highest 1/3 of the waves (individual waves may be more than twice the significant wave height). Maximum and minimum significant wave height values are indicated as necessary.

Coverage

The National Hurricane Center produces wind/wave forecasts covering the following areas:

1. Atlantic (from the equator to 31°°N between 35°W and 100°W, including the Pacific east of 100°W)
2. East Pacific (from 20°S to 30°N east of 145°W)

Issuance/Transmission

The Wind/wave forecasts are transmitted by radiofax via New Orleans, Pt. Reyes, and Honolulu according to the following table:

Surface Forecasts

Purpose

Surface forecasts are produced to depict the 24-, 48-, and 72-hour forecasts of sea level pressure and surface features over the tropical and subtropical Atlantic and East Pacific waters.

Content

The surface forecasts include the forecast sea level pressure field depicted by isobars contoured every four millibars (mb). Intermediate two millibar isobars are sometimes included in areas where the pressure gradient is relatively light. Relevant surface features are also shown, including areas of high and low pressure, frontal systems (cold, warm, stationary, and occluded), troughs, ridges, drylines, tropical waves, and tropical cyclones. The 72-hour forecast chart also includes a depiction of the 96-hour forecast positions of highs, lows, and tropical cyclones.

Coverage

The National Hurricane Center produces surface forecasts covering the following areas:

1. Atlantic (from the equator to 31°N between 35°W and 100°W, including the Pacific east of 100°W)
2. East Pacific (from 20°S to 30°N east of 145°W)

Issuance/Transmission

The surface forecasts are transmitted by radiofax via New Orleans and Honolulu according to the following table:

Peak Wave Period and Direction Forecasts

Purpose

Peak wave period and direction forecast charts are produced to depict the 48- and 72-hour forecasts of how much time exists between the most energetic waves and what direction these waves are coming from over the tropical and subtropical Atlantic and East Pacific waters.

Content

The peak wave period (in seconds) is defined as the wave period associated with the most energetic waves in the total wave spectrum at a specific point. Wave regimes that are dominated by wind waves tend to have smaller peak wave periods, and regimes that are dominated by swell tend to have larger peak wave periods. It is important to note that these charts only depict the peak wave period and that there still could be other significant waves at a specific point that just happen to have less energy. Peak wave periods are contoured by isolating different swell events with a single line – not contouring at a specific interval as in other forecast graphics. Labels within the contours indicate the peak wave period in that general area. Arrows are also shown depicting the direction that the most energetic waves are traveling.

Coverage

The National Hurricane Center produces peak wave period and direction forecasts covering the following areas:

1. Atlantic (from the equator to 31°N between 35°W and 100°W, including the Pacific east of 100°W)
2. East Pacific (from 20°S to 30°N east of 145°W)

Issuance/Transmission

The peak wave period and direction forecasts are transmitted by radiofax via New Orleans, Pt. Reyes, and Honolulu according to the following table:

Tropical/Subtropical Cyclone Position and Intensity Estimates

TAFB provides the National Hurricane Center with position estimates of tropical cyclones every three hours and intensity estimates every six hours. Intensity estimates use the Dvorak technique, which is a statistical system using observed satellite cloud pattern and a set of rules to produce a current estimate of a cyclone's strength. Estimates can be made from both visible and infrared satellite imagery. The Dvorak technique is the main tool for determining tropical cyclone strength when it is out of range of reconnaissance aircraft.

TAFB also provides NHC with position and intensity estimates for subtropical cyclones (a hybrid between tropical cyclones and frontal or extratropical cyclones) using the Herbert-Poteat technique.

TAFB's position and intensity estimates are not currently available to the public. However, the intensity estimates (called T numbers, CI numbers, and ST numbers), are often referred to in NHC's Tropical Cyclone Discussions and Preliminary Reports. The following table (taken from the reports mentioned below) gives the approximate wind and pressure values for the CI and ST numbers.

NHC uses the Atlantic pressure table for eastern Pacific tropical cyclones. Note that these are intensity estimates and may be superceded by reconnaissance and/or surface observations.

More information on the Dvorak technique is found in NOAA Technical Report NESDIS 11 - Tropical Cyclone Intensity Analysis Using Satellite Data - by Vernon F. Dvorak. More infomation on the Herbert-Poteat technique is found in NOAA Technical Memorandum NWS SR-83 - A Satellite Classification Technique for Subtropical Cyclones - by Paul J. Herbert and K.O. Poteat.

TAFB is currently testing an objective version of the Dvorak technique. This could provide intensity estimates every 30 minutes. More information can be obtained from Ray Zehr at the Cooperative Institute for Research in the Atmosphere, Colorado St. University, or from Chris Velden or Tim Olander at the Cooperative Insititute for Meteorological Satellite Studies, University of Wisconsin.

Marine Radiofax Broadcast Schedule

The Tropical Analysis and Forecast Branch (TAFB) provides marine analyses and forecasts for the Gulf of Mexico, Caribbean Sea, and the tropical and subtropical Atlantic and Pacific. Products available include: surface analyzes, sea state analyses, wind/seas forecasts, wave period/swell direction forecasts, tropical cyclone danger area forecaasts (during the hurricane season), text High Seas Forecasts, and GOES satellite imagery. These products are transmitted through the U.S. Coast Guard Stations at New Orleans, Louisiana, and Pt. Reyes, California. These and other Tropical Prediction Center products are also available from the National Weather Service Marine Fax page. Here is more information on receiving NWS marine products at sea.

The complete list of radiofax broadcasts can be found on the TAFB Radiofax Broadcast Schedule page.