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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.
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:
Coverage and intensity for convective and non-convective weather is defined as follows:
COVERAGE FOR CONVECTIVE and NON-CONVECTIVE WEATHER:
Numerous | Widespread | >54% |
Scattered | Areas | 25% - 54% |
Widely scattered | Local/Locally | <25% |
Isolated | No %, implies circumnavigability |
COVERAGE FOR SIGNIFICANT CLOUDS:
Clear | 0 |
Few | 1/8 - 2/8 |
Scattered | 3/8 - 4/8 |
Broken | 5/8 - 7/8 |
Overcast | 8/8 |
INTENSITY OF CONVECTION (based on cloud top temperatures):
Strong | < -70°C (summer) | < -60°C (winter) |
Moderate | between -45°C and -70°C (summer) | between -35°C and -60°C (winter) |
Weak | > -45°C (summer) | > -35°C (winter) |
The National Hurricane Center issues two Tropical Weather Discussions, as shown below:
WMO | NWWS | |
---|---|---|
Atlantic | AXNT20 KNHC | MIATWDAT |
East Pacific | AXPZ20 KNHC | MIATWDEP |
Issuance Time | |||||
MIATWDAT | 105 AM EST (205 AM EDT) |
705 AM EST (805 AM EDT) |
105 PM EST (205 PM EDT) |
705 PM EST 805 PM EDT) |
|
---|---|---|---|---|---|
MIATWDEP | 0405 UTC | 1005 UTC | 1605 UTC | 2205 UTC |
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 and XII, which cover most of the North Atlantic Ocean and North Pacific Ocean. On June 30, 2017, NHC transferred forecast responsibility for the Southeast Pacific Ocean (METAREA XVI) to Peru. These forecasts can be found at https://www.dhn.mil.pe/metareaoceanica and https://www.dhn.mil.pe/metareacostera. NHC will retain forecast backup resonsibility for the Southeast Pacific high seas forecast (HSFEP3) in the event Peru is unable to compose and transmit the product.
The National Hurricane Center issues three High Seas Forecasts for parts of METAREAS IV and XII. 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.
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):
Primary Headers | Alternate Headers | |||
---|---|---|---|---|
WMO | NWWS | WMO | NWWS | |
Atlantic | FZNT02 KNHC | MIAHSFAT2 | FZNT01 KWBC | NFDHSFAT1 |
Northeast Pacific | FZPN03 KNHC | MIAHSFEP2 | FZPN01 KWBC | NFDHSFEPI |
Southeast Pacific (Backup) | FZPN04 KNHC | MIAHSFEP3 | (WMO Peru) FQPR01 SPIM |
High seas products are issued on a regular six hourly schedule as shown below:
Issuance Time in UTC | ||||
---|---|---|---|---|
MIAHSFAT2 | 0430 | 1030 | 1630 | 2230 |
MIAHSFEP2 | 0430 | 1030 | 1630 | 2230 |
MIAHSFEP3 (Backup) | 0515 | 1115 | 1715 | 2315 |
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.
See table for the latest High Seas ForecastThe Tropical Analysis and Forecast Branch (TAFB) of the National Hurricane Center (NHC) provides forecast and warning information to mariners who travel on the oceanic waters adjacent to the U.S. and its territorial coastal waters in the Gulf of Mexico, Caribbean Sea, and portions of the tropical and subtropical North Atlantic Ocean. The primary alphanumeric product issued by the NHC/TAFB for this purpose is the Offshore Waters Forecast, serving users who operate from the coastal waters out several hundred nautical miles from shore. The Offshore Waters Forecast complements the higher resolution Coastal Waters Forecast produced by local National Weather Service forecast offices and cover the U.S. territorial waters from the coast out to 60 nm offshore.
The Offshore Waters Forecasts cover the Gulf of Mexico, Caribbean Sea, and portions of the Atlantic Ocean south of 31°North and west of 55° West. This area is divided into 32 zones designed in part to take into account the regional marine climatology. The configuration of the Offshore Waters Marine zones is shown on the map below:
There are three Offshore Waters Forecast provided by the NHC/TAFB. The MIAOFFNT3 (WMO header FZNT23 KNHC) covers the Caribbean Sea, and the Tropical North Atlantic south of 19° North. The MIAOFFNT4 (WMO header FZNT24 KNHC) encompasses the Gulf of Mexico. The MIAOFFNT5 (WMO header FZNT25 KNHC) covers the Southwest North Atlantic north of 19° North.
These Offshore Waters Forecasts provide mariners with a general overview of large scale environmental marine conditions out five days, to include winds, seas, and major weather impacts. Marine warnings such as gale warnings or warnings for tropical storms or hurricanes will be headlined for each affected zone through the first 36 hours of the forecast period. In addition, brief, plain-language synopses are included in the forecast for the Gulf of Mexico, the Caribbean Sea and Tropical Atlantic, and the Southwest North Atlantic areas.
Winds represent predominant conditions at 10 meters above the surface of the water. Wind direction is described by the eight points of the compass.
Sea state is described in terms of "significant wave height" which is defined in the NWS Glossary as .the mean or average height of the highest one third of all waves in a swell train or in a wave generating region. It approximates the value an experienced observer would report if visually estimating sea height.. Seas will typically be expressed in terms of a range (e.g. 2 to 4 ft). This is to represent uncertainty in the forecast, especially considering the large areas of each marine zone. In fact, it is important to emphasize that there is a broad spectrum of wave heights at any given time in any part of the ocean, and individual wave heights may be twice the significant wave height. In addition to significant wave height, dominant swell and direction are described as needed.
The Offshore Waters Forecast also includes weather impacts whenever they are expected to pose a danger to navigation. This may be in the form of widespread areas of fog, smoke, or volcanic ash that limit visibility, or large clusters of moderate to strong thunderstorms.
Marine Zone Names and Universal Geographic Codes (UGC's)
Although not technically marine zones, the Synopsis paragraphs also have assigned UGC's as shown below:
Synopses
UGC | Synopsis Name |
---|---|
AMZ001 |
Synopsis for the Caribbean and Tropical N Atlantic from 07N to 19N between 55W and 64W |
AMZ101 |
Synopsis for the SW N Atlantic including the Bahamas |
GMZ001 |
Synopsis for the Gulf of Mexico |
Offshore waters products are transmitted under World Meteorological Organization (WMO) and NOAA Weather Wire Services (NWWS) headers as shown in the following table:
WMO | NWWS | |
---|---|---|
Caribbean Sea and Tropical North Atlantic |
FZNT23 KNHC | MIAOFFNT3 |
Gulf of Mexico Forecast | FZNT24 KNHC | MIAOFFNT4 |
Southwest North Atlantic | FZNT25 KNHC | MIAOFFNT5 |
Offshore waters products are issued on a regular six hourly schedule as shown below:
Issuance Time | |||||
---|---|---|---|---|---|
MIAOFFNT3 MIAOFFNT4 MIAOFFNT5 |
430 AM EST (530 AM EDT) 430 AM EDT |
1030 AM EST (1130 AM EDT) 1030 AM EDT |
430 PM EST (530 PM EDT) 430 PM EDT |
1030 PM EST (1130 PM EDT) 1030 PM EDT |
The International Maritime Organization has designated NAVTEX as the primary means for transmitting coastal urgent marine safety information to ships worldwide. In the United States, NAVTEX is broadcast from Coast Guard facilities in Cape Cod, MA; Chesapeake, VA; Savannah, GA; Miami, FL; New Orleans, LA; San Juan, PR; Cambria, CA; Pt. Reyes, CA; Astoria, OR; Kodiak, AK; Honolulu, HI and Guam. The Coast Guard began operating NAVTEX from Boston in 1983.
NAVTEX coverage is reasonably continuous along the east, west and Gulf coasts of the United States, as well the area around Kodiak, Alaska; Guam and Puerto Rico. The U.S. has no coverage in the Great Lakes, though coverage of much of the Lakes is provided by the Canadian Coast Guard.
NHC/TAFB is responsible for producing three NAVTEX forecasts transmitted from New Orleans, Miami, and San Juan. The broadcast includes a synopsis which describes 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 system. 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 NAVTEX 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 36 hours of the forecast.
NAVTEX forecasts are similar to the Offshore Waters Forecasts, but differ in some in important aspects. Since the NAVTEX zones were designed to accommodate the listening area of their respective transmitters, they are configured differently than the more comprehensive Offshore Waters Forecast zones. The content of both forecasts relates to the same weather elements, covering similar areas, over the same times. However, the NAVTEX forecast differ from the Offshore Waters Forecast in that the NAVTEX zones include coastal areas within 60 nm of the shore, whereas the Offshore Waters Forecasts do not. NAVTEX forecast are required to be less than 89 lines, sometimes limiting the amount of detail that can be included. While Offshore Waters Forecasts are concise, there is no similar limitation to text length. Thus, NAVTEX forecast tend to be of a lower resolution than the Offshore Waters Forecasts. This can result in slight difference in wording between the two products. Warning information will be exactly the same for each forecast, however.
Each of the three NAVTEX forecasts produced by NHC/TAFB are described below, along with a map displaying each forecast area: TAFB issues three separate NAVTEX Forecasts, as shown below with the following AWIPS/WMO headers:
Transmitter | Product Identifiers | Description of Area |
---|---|---|
Miami, FL | FZNT25 KNHC, MIAOFFN04 | Flagler Beach, FL to Suwanne River, FL out 200 nm |
San Juan, PR | FZNT26 KNHC, MIAOFFN05 | 200 nm surrounding San Juan, PR |
New Orleans, LA | FZNT27 KNHC, MIAOFFN06 | Suwanee River, FL to Rio Grande out 200 nm |
NAVTEX is an international automated medium frequency (518 kHz) direct-printing service for delivery of navigational and meteorological warnings and forecasts, as well as urgent marine safety information to ships. It was developed to provide a low-cost, simple, and automated means of receiving this information aboard ships at sea within approximately 200 nautical miles of shore. NAVTEX stations in the U.S. are operated by the U.S. Coast Guard. There are no user fees associated with receiving NAVTEX broadcasts. Within the U.S., there are no current plans to broadcast NAVTEX on the alternate designated frequencies of 490 or 4209.5 kHz.
NAVTEX is a major element of the Global Marine and Distress Safety System (GMDSS). For further information on NAVTEX, the GMDSS, and worldwide NAVTEX schedules, including coverage diagrams, visit the U.S. Coast Guard Maritime Telecommunications Information webpage. Daily issuance times (in UTC) for each broadcast are 0345, 0945, 1545, and 2145.
See table for the latest NAVTEX Marine ForecastsThe U.S. Coast Guard provides basic weather information from the National Weather Service in the form of routine High Frequency voice broadcasts (also known as "VOBRA") in order to provide service to vessels operating in areas beyond the range of coastal NOAA Weather Radio stations. This information is prepared cooperatively by the Ocean Prediction Center, National Hurricane Center and Honolulu Forecast Office.
There are three Offshore Waters Forecast provided by the NHC/TAFB. The MIAOFFNT3 (WMO header FZNT23 KNHC) covers the Caribbean Sea, and the Tropical North Atlantic south of 19° North. The MIAOFFNT4 (WMO header FZNT24 KNHC) encompasses the Gulf of Mexico. The MIAOFFNT5 (WMO header FZNT25 KNHC) covers the Southwest North Atlantic north of 19° North.
The two VOBRA forecasts provide mariners with a general overview of large scale environmental marine conditions out five days, to include winds, seas, and major weather impacts. Marine warnings such as gale warnings or warnings for tropical storms or hurricanes will be headlined for each affected zone through the first 36 hours of the forecast period. In addition, brief, plain-language synopses are included in the forecast for the Gulf of Mexico, the Caribbean Sea and Tropical Atlantic, and the Southwest North Atlantic areas.
Winds represent predominant conditions at 10 meters above the surface of the water. Wind direction is described by the eight points of the compass.
Sea state is described in terms of .significant wave height. which is defined in the NWS Glossary as .the mean or average height of the highest one third of all waves in a swell train or in a wave generating region. It approximates the value an experienced observer would report if visually estimating sea height.. Seas will typically be expressed in terms of a range (e.g. 2 to 4 ft). This is to represent uncertainty in the forecast, especially considering the large areas of each marine zone. In fact, it is important to emphasize that there is a broad spectrum of wave heights at any given time in any part of the ocean, and individual wave heights may be twice the significant wave height. Unlike the Offshore Waters Forecasts, the VOBRA forecasts do not include swell information. This is due the limited broadcast times available.
The VOBRA forecasts also include weather impacts whenever they are expected to pose a danger to navigation. This may be in the form of widespread areas of fog, smoke, or volcanic ash that limit visibility, or large clusters of moderate to strong thunderstorms.
TAFB issues two VOBRA text forecasts, as shown below with the following AWIPS/WMO headers:
AWIPS/WMO Identifiers
Identifiers | Description of Area |
---|---|
FZNT31 KNHC/MIAOFFN20 | Caribbean Sea and portions of the Western Atlantic Ocean South of 31° North |
FZNT32 KNHC/MIAOFFN21 | Gulf of Mexico |
AWIPS Header MIAOFFN20 - WMO Header FZNT31 KNHC
Area of coverage: Caribbean Sea, Southwest North Atlantic (south of 31°North and west of 65° West) and the Tropical North Atlantic (from 07°North to 19°North west of 55°West) and includes the following combination of the offshore waters zones in the Caribbean Sea and Tropical North Atlantic Ocean
and the southwest North Atlantic
Combination of offshore zones for the MIAOFFN20 VOBRA text product.
AWIPS Header MIAOFFN21 - WMO Header FZNT32 KNHC
Area of coverage: Gulf of Mexico and includes the following combination of the offshore waters zones in the Gulf of Mexico Portions of Offshore Waters Forecasts parsed into the Broadcast:
Combination of offshore zones for the MIAOFFN21 VOBRA text product.
The transmissions originate from six sites located around the country and the transmission range is dependent upon operating frequency, time of day and atmospheric conditions and can vary from only short distances to several thousand miles. Best reception can be achieved by proper selection of frequency and an adequate antenna system. HF Voice Broadcasts covering TAFB's marine area of responsibility are conducted by the USCG from transmitter sites in Chesapeake, VA, and (New Orleans) Belle Chase, LA. See table below for station broadcast schedules.
HF Voice Broadcast Schedule
Zone forecast broadcast times indicated by orange shading. High Seas forecast broadcast times indicated by unshaded times.
Chesapeake (NMN)
Frequency | Time (UTC) | |||||||
---|---|---|---|---|---|---|---|---|
4426, 6501, 8764 kHz (USB) | 0330 | 0515 | 0930 | |||||
6501, 8764, 13089 kHz (USB) | 1115 | 1530 | 2130 | 2315 | ||||
8764, 13089, 17314 kHz (USB) | 1715 |
New Orleans (NMG)
Frequency | Time (UTC) | |||||||
---|---|---|---|---|---|---|---|---|
4316, 8502, 12788 kHz (USB) | 0330 | 0515 | 0930 | 1115 | 1530 | 1715 | 2130 | 2315 |
See table for the latest HF Voice Broadcasts
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.
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.
The Pan-American Temperature and Precipitation Table includes the following stations (as shown in the map above):
Acapulco, Mexio | Merida, Mexico |
Barbados | Mexico City, Mexico |
Bermuda | Montego Bay, Jamaica |
Bogotá, Colombia | Monterrey, Mexico |
Curaçao, Netherlands Antilles | Nassau, Bahamas |
Freeport, Bahamas | San Juan, Puerto Rico |
Guadalajara, Mexico | St. Thomas, Virgin Islands |
Guadeloupe | Tegucigalpa, Honduras |
Havana, Cuba | Trinidad |
Kingston, Jamaica | Veracruz, Mexico |
Mazatlán, Mexico |
The Pan-American Temperature and Precipitation Table is transmitted under World Meteorological Organization (WMO) and NOAA Weather Wire Services (NWWS) headers as shown below:
WMO | NWWS | |
Pan-Am Table | SXCA01 KNHC | MIATPTPAN |
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) |
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.
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.
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:
The NWS Unified Surface Analysis is created by merging the separate surface analysis produced by the National Hurricane Center, the Weather 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.
The Tropical Surface Analysis is transmitted by radiofax via New Orleans, Pt. Reyes, and Honolulu according to the following table:
New Orleans, LA (East Half) |
New Orleans, LA (West Half) |
Pt. Reyes, CA | Honolulu, HI | |||||
---|---|---|---|---|---|---|---|---|
Valid Time (UTC) |
Transmit Time (UTC) |
Filename | Transmit Time (UTC) |
Filename | Transmit Time (UTC) |
Filename | Transmit Time (UTC) |
Filename |
0000 | 0620 | PYEA86.TIF | 0605 | PYEB86.TIF | 0408 | PYFA96.TIF | 0356 | PYFA96.TIF |
0600 | 1220 | PYEA87.TIF | 1205 | PYEB87.TIF | 0945 | PYFA97.TIF | 0954 | PYFA97.TIF |
1200 | 1820 | PYEA85.TIF | 1805 | PYEB85.TIF | 1608 | PYFA98.TIF | 1556 | PYFA98.TIF |
1800 | 0020 | PYEA88.TIF | 0005 | PYEB88.TIF | 2150 | PYFA99.TIF | 2154 | PYFA99.TIF |
latest | PYEA11.TIF | PYEB11.TIF | PYFA90.TIF | PYFA90.TIF |
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.
See table for the latest Tropical Surface Analysis
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Page last modified: Tuesday, 26-Mar-2024 18:24:08 UTC