Marine Weather Review-Tropical Atlantic and Tropical East Pacific Areas July through December 2004Daniel P. Brown and Hugh D. Cobb III, Tropical Analysis and Forecast Branch,
Tropical Prediction Center, NOAA/NWS Miami, Florida
A Brief Overview of the Tropical Prediction Center's (TPC) Tropical Analysis and Forecast Branch.
The Tropical Analysis and Forecast Branch (TAFB) is one of three branches of NOAA's Tropical Prediction Center (TPC). The other branches are the Hurricane Specialist Unit and the Technical Support Branch (TSB). TAFB is responsible for issuing marine forecasts for the tropical and subtropical Atlantic Ocean, Caribbean Sea, Gulf of Mexico, and the tropical and subtropical areas of the eastern Pacific Ocean (Figure 1). In order to complete the assigned duties, TAFB maintains three operational forecast desks 24 hours each day, 365 days per year. One operational desk is responsible for the surface analysis, Atlantic Tropical Weather Discussion, and peak wave period/peak swell direction forecast charts. The other two forecast desks are divided by forecast basin with an Atlantic and Pacific forecaster responsible for the products for each respective area.
Each day, TAFB forecasters issue a total of 32 marine text forecasts. These include three separate High Seas (Atlantic, northeast Pacific, and southeast Pacific) and NAVTEX forecasts four times daily. The High Seas Forecasts only include areas of wind greater than 20 kts and seas 8 ft or higher. These marine forecasts are tailored towards larger ships that spend days to weeks at sea. TAFB also composes a more detailed Offshore Waters Forecast for the Gulf of Mexico, Caribbean Sea, and the southwest and tropical North Atlantic four times daily. These more detailed forecasts are geared toward smaller vessels that may venture offshore for a few days at a time. A detailed description of each of these marine forecast products is available at www.nhc.noaa.gov/abouttafbprod.shtml. Forecasters also produce a Marine Weather Discussion for the offshore area twice daily. The discussion describes weather features that are or will be affecting the forecast area during the next 5 days. Meteorologists routinely discuss differences or similarities in the numerical models that they are basing their forecast on. They may also reference current ship, buoy or QuikSCAT data that have influenced the forecast. By reading the discussion one may get a better understanding of the confidence level that the forecasters has placed on his or her forecast. TAFB meteorologists (Figure 2) also write Tropical Weather Discussions for the Atlantic and East Pacific areas. These discussions tend to provide a detailed description of the atmosphere in general and are usually less focused on marine weather. However, since there is no Marine Weather Discussion for the eastern Pacific, forecasters will occasionally highlight significant marine events in the East Pacific Tropical Weather Discussion. These significant events may include gale or storm force winds in the Gulf of Tehuantepec or strong wind events in the Sea of Cortez or Gulf of Papagayo.
If the saying, "a picture is worth a thousand words" is correct, then TAFB's 45 graphical analysis and marine forecast products issued daily must provide mariners with a great deal of valuable information. TAFB issues a surface analysis every six hours for the tropical and subtropical Atlantic and eastern Pacific Oceans. TAFB meteorologists also provide 3-hourly surface analyses for Florida, the Gulf of Mexico and Mexico for a large surface weather map that is issued by the Hydrometeorological Prediction Center in Washington, D.C. Additionally, a sea-state analysis is completed at 0000 and 1200 UTC each day for the tropical and subtropical Atlantic basin. When producing both the surface and sea-state analysis the meteorologists are relying on all available ship data. The VOS ship data is an extremely important tool that can be used to determine the location of weather features such as troughs, fronts, lows and highs. This ship data is also valuable "ground truth" that helps the forecaster to evaluate numerical forecast model output. Being able to determine model performance helps the forecaster produce much more accurate forecasts and warnings.
TAFB's graphical marine forecast products include 24, 48, and 72 hour wind/wave (Figure 3,) and surface pressure forecasts for both the Atlantic and east Pacific Basins. The wind/wave forecast provides a prediction of surface winds and sea heights across the basin. Forecast positions of weather features such as fronts, troughs, lows, highs, tropical cyclones, and gale or storm warning areas are depicted. The surface pressure forecast also includes forecast positions of the significant weather features and areas of gale or storm force winds. All of these graphical forecasts are issued twice daily, except the 24 hour wind/wave chart which is issued 4 times daily.
Figure 4 is a Graphical Product Legend that explains how to interpret the wind barbs on the wind/wave charts and also provides definitions for each symbol or abbreviation used on the products. Additional marine graphics include the Tropical Cyclone Danger Graphic which depicts a tropical cyclone's forecast track and area of possible danger. The area of "danger" is computed using the 1-2-3 rule which adds 100, 200, and 300 nmi to the 34 kts wind radii at the 24, 48, and 72 hour forecast positions. The Danger Graphic also includes areas of possible tropical cyclone formation within the next 36 hours. Outside of hurricane season the Danger Graphic becomes a High Wind and Associated Seas Graphic which depicts current areas of high wind over the Atlantic and Pacific Oceans. The suite of graphical marine products that TAFB produces is available via RadioFAX and on the world wide web on both the TAFB (www.nhc.noaa.gov/forecast.shtml) and National Weather Service (www.nws.noaa.gov/marine) sites. Table 1 is the current New Orleans RadioFAX broadcast schedule which includes all the graphical forecasts TAFB issues for the Atlantic, Caribbean, and Gulf of Mexico. TAFB's eastern Pacific forecasts are available on the Pt. Reyes or Honolulu RadioFAX broadcast. These schedules are available on the world wide web at www.nws.noaa.gov/om/marine/radiofax.htm.
TAFB is also responsible for several tropical cyclone related products in support of the TPC/National Hurricane Center (NHC) tropical cyclone forecast and warning program. TAFB meteorologists use the Dvorak Technique to estimate the position and intensity of both active and developing tropical cyclones (Figure 5). The Dvorak estimates are routinely provided to the NHC Hurricane Specialists who use them to help determine the strength and location of a tropical cyclone. Forecasters at TPC/NHC have been using the Dvorak Technique for over 30 years to help determine a tropical cyclone's intensity. The intensity estimates are based on the organizational structure of the storm. This may include the amount of thunderstorm banding which wraps around the center or how distinct the eye of a hurricane is. These intensity estimates are extremely important when a storm is too far from land for reconnaissance aircraft to fly into. Beginning in 2004, TAFB forecasters also provided position estimates for tropical storms and hurricanes from microwave satellite imagery. Microwave images are a relatively new form of data that is obtained from several polar-orbiting satellites. The microwave imager on the satellites can "peer" through clouds to help the forecaster determine the center location and the overall storm structure.
During the peak of the season, between August 1 and mid-October, TAFB meteorologists work with the Hurricane Specialists as Hurricane Support Meteorologists (HSM). The HSM's provide forecast support to the NHC Hurricane Specialists. HSM's will aid in gathering and analyzing surface, ship, satellite, and reconnaissance data. They also provide tropical cyclone center location estimates from radar once a system is close enough to land to be tracked. During busy times HSM's also provide media and forecast support. During the busy 2004 hurricane season, HSM's aided in the preparation of a number of tropical cyclone forecast advisory packages when multiple storms were occurring across the Eastern Pacific and Atlantic basins.
In addition, to performing regular forecast duties, most TAFB meteorologists work on research projects or computer applications that can help to produce more useful and accurate forecasts. With such a large and diverse area of forecast responsibility, TAFB forecasters stay very busy developing all these forecast and analysis products. Hopefully, this brief look into TAFB operations has provided a better understanding the forecast responsibilities of TAFB and of our job as marine forecasters. If you have any questions or comments about TAFB or our products please feel free to contact Christopher Burr (Christopher.A.Burr@noaa.gov), chief of the TAFB, or Daniel Brown (Daniel.P.Brown@noaa.gov). We would be happy, as time permits, to answer your correspondence. Here's to fair winds and following seas in your journeys.
Significant Weather of the Period
Please refer to the articles on the 2004 Atlantic and Eastern North Pacific Hurricane Season for information about tropical systems during this past hurricane season. This article will provide a brief review of non-tropical weather systems that produced significant weather across the tropical and subtropical regions of the Atlantic and Eastern Pacific during the second half of 2004.
Atlantic, Caribbean and Gulf of Mexico:
A total of seven non-tropical gale events occurred over the tropical and subtropical Atlantic, Caribbean and Gulf of Mexico from July through December 2004 (Table 2). The first event of the fall and winter season occurred a couple weeks later than normal. Thereafter, three separate cold fronts produced gales over the Gulf of Mexico or Atlantic in November and December. Two lows also produced gales in the subtropical Atlantic during the period. The first low developed on the 25 November and produced gale force winds south of 31N from 27-30 November. This low transitioned from an extra-tropical low into Tropical Storm Otto on 30 November. Please refer to the article on the 2004 Atlantic Hurricane Season for more information on Otto. The most significant event of the period occurred between 25-27 December. This event was produced by a strong low that developed over the Gulf of Mexico. This low created near storm force conditions over the Gulf.
Gulf of Mexico and western Atlantic Low 25-27 December: The stage was set for this rather unusual event on the 22 December as a strong cold front moved into the northwestern Gulf of Mexico. The front moved southeastward across the western and middle Gulf on 23 December. At 1200 UTC 24 December, the front extended from central Florida to the southern Bay of Campeche. The front continued to move slowly southward over the Florida peninsula but became stationary over the southern Gulf of Mexico. A strong mid- to upper-level low pressure system moving across northern Mexico and southern Texas aided in the development of a surface low along the stationary front over the south-central Gulf of Mexico late on the 24th.
As the low strengthened, gale force winds began blowing west of the low over the western Gulf of Mexico early on the 25 December. The ships Deepwater Horizon (H3SM) and Frances L (C6YE) both observed 35 kts winds in the central Gulf of Mexico at 0600 and 1200 UTC respectively. By 1400 UTC, NOAA buoy 42002 (25.2N 94.4W) in the western gulf reported 35 kts winds and sea heights that peaked at 6 m (20 ft). The low continued to slowly strengthen and, by 1800 UTC, was analyzed over the central Gulf of Mexico near 25N 89.5W (Figure 6). At this time, the ship Deepwater Millennium (3FJA9) observed 37 kts winds over the north-central Gulf. As the low moved slowly east-northeastward, winds at the middle Gulf NOAA buoy 42001 (25.8N 89.7W) became north-northwest and increased to gale force at 1900 UTC. The winds at the buoy increased to 45 kts with gusts to 58 kts at 2000 UTC. At 0000 UTC 26 December, the low was just northwest of the eastern Gulf NOAA buoy 42003 (26N 85.9W). Winds at the buoy increased to gale force by 0100 UTC. Between 0400 and 0600 UTC winds at the buoy peaked at 45 kts with gusts to 56 kts.
Between 0600 and 0900 UTC 26 December, the low moved across the Florida peninsula, entering the west coast just north of Tampa Bay, then exiting the east coast near Daytona Beach. Once the low moved into the Atlantic, gale force winds began blowing off the northeast Florida coast. NOAA's Atlantic buoys 41009 (28.5N 80.2W), 41010 (28.9N 78.5W), and 41012 (30.0N 80.6W), all reported 35 to 40 kts wind with gusts to around 45 kts. By 1800 UTC, the low was centered off the coast of North Carolina with a cold front trailing south across the central Bahamas and eastern Cuba. The low continued to move northeastward away from the area and gale conditions ended south of 31N by 0000 UTC 27 December.
With cold arctic air in place along the Gulf Coast, this event not only produced gale to near storm force winds over the Gulf of Mexico, but also brought snow and sleet to portions of the southeastern United States on Christmas Day. The snow event will be remembered for many years across south Texas, because it produced an historic white Christmas from the Houston-Galveston area south to Brownsville and into northern Mexico. The snow that accumulated at Brownsville was the first since February 1895. The event also set new all-time snowfall records of 4.4 inches at Corpus Christi and 12.5 inches at Victoria. Figure 7 includes two visible satellite images from the 25th and 26th December that show the snow cover over southeast Texas. Snow and sleet also fell along the northern Gulf coast from Louisiana to the western Florida Panhandle. Significant snow also accumulated across eastern portions of North Carolina and Virginia on the 26th.
Eastern North Pacific
The first Gulf of Tehuantepec gale event of the season began in early November. Once the Tehuantepec season began, the events occurred quite regularly during November and December. A total of seven Gulf of Tehuantepec gale events occurred during the period. Storm force winds were observed during three of these events. Table 3 is a list of the estimated beginning and ending times of Gulf of Tehuantepec gale and storm events between July and December 2004. These events were verified by either a reliable ship observation or timely Quikscat data.
Gulf of Tehuantepec Events: The first Gulf of Tehuantepec event began around 1800 UTC 3 November and lasted for nearly a week. A QuikSCAT pass on 2344 UTC 3 November was the first confirmation of a gale event, with 40 kts wind indicated in the Gulf of Tehuantepec. As a result of the long duration of this event, there were several ships which reported gale force winds. The first report was at 1800 UTC 4 November when the ship Maersk Rio Grande (ZDFK7) reported north-northeast winds of 45 kts and 13 ft seas while located near 15 N 95 W. At 0600 UTC 6 November, another ship Mette Maersk (OXKT2) reported northeast winds of 45 kts while located near 14.5N 96.5W. The gale warning was upgraded to a storm warning at 1630 UTC 6 November based on a 1201 UTC 6 November QUIKSCAT pass, which indicated several 50 kts wind barbs at the 25 km resolution (Figure 8). Shortly after the upgrade to a storm event, another ship, the HMI Brenton Reef (WCY8453), reported northerly winds of 40 kts and 4 m (14 ft) seas while located near 14.5N 94.3W. The ship was traversing westward through the high wind swath and reported northeast winds of 40 kts six hours later while located near 15N 95.5W. At 1200 UTC 8 November, the Paris Express (DIHE) reported northeasterly winds of 40 kts and seas of 4.5 m (15 ft) near 14N 95.5W. The last ship report of gale force winds was at 1200 UTC 9 November when the ship Aida (SCFI) reported 35 kts winds near 13N 95W. Six hours later, the winds had dropped off to 30 kts as the ship progressed westward to near 14N 96.7W.
The second wind event was of much shorter duration, lasting only 30 hours from 1200 UTC 25 November to 1800 UTC 26 November. A 1209 UTC QUIKSCAT pass indicated 35-40 kts winds at the head of the Gulf of Tehuantepec. The next pass around 0041 UTC 26 November detected a small area of 35 kts winds in the Gulf of Tehuantepec.
The next wind event commenced a week later around 1200 UTC 1 December and lasted about 72 hours. As in the previous event, scatterometer data barely indicated gale force winds for the two passes, at 1202 UTC 2 December and 1202 UTC 3 December. At 1800 UTC 1 December, the Star Harmonia (LAGB5) located near 14.5N 95W reported north-northeast winds of 35 kts and seas of 4.5 m (15 ft). This was the only ship report during this event.
The fourth wind event for the Gulf of Tehuantepec began around 0600 UTC 11 December and continued until 1800 UTC 12 December. An 1155 UTC 11 December QUIKSCAT pass indicated 35 kts winds in the area. A later pass at 0026 UTC 12 December indicated 35-40 kts winds. At 1800 UTC 11 December, Zim Israel (4XGX) reported north-northeast winds of 40 kts and a combined sea of 4.5 m (15 ft) while located near 14N 96.3W. Six hours later, the same ship reported north winds of 40 kts and 4.5 m (15 ft) seas as it traversed eastward to near 13.7N 94.5W.
The fifth wind event of the 2004-2005 Gulf of Tehuantepec season began at 0600 UTC 14 December and continued until 1800 UTC 16 December. This event was the first of two consecutive storm events to occur in mid-December. A 1217 UTC 14 December QUIKSCAT Pass indicated 50 kts winds in the Gulf of Tehuantepec. Subsequent passes at 0049 UTC and 1151 UTC 15 November indicated a larger area of 50 kts winds in the Gulf of Tehuantepec region. The only ship report of gale force winds was on 1200 UTC 14 December when the Dagmar Maersk reported 35 kts winds and 3 m (10 ft) seas while located near 13N 97W. The next storm event came quickly on the heels of the first, commencing near 0000 UTC 18 December and continuing for 84 hours until 1200 UTC 21 December. 35 kts winds were indicated on the 1214 UTC 18 December QUIKSCAT pass. The only ship report of gale force winds or greater during this event came from the Green Point (WCY4148) at 1200 UTC 20 December. The ship reported north-northeasterly winds of 40 kts but no sea heights while located near 13.5N 95W. Six hours later the same ship traversed into the heart of the high wind swath near 14N 96W and reported winds of 45 kts and seas of 5 m (16 ft).
The last wind event for the calendar year 2004 began around 0000 UTC 26 December and was associated with strong high pressure which built southward over the Gulf of Mexico in the wake of the historic Christmas snow event on the Texas coast (see Atlantic section). This event lasted for more than 4 days before ending at 1800 UTC 30 December. The 1207 UTC 26 December QUIKSCAT pass indicated 50 kts winds. Subsequent passes at 0038 UTC and 1141 UTC 27 December indicated winds had decreased to 40-45 kts. There were quite a number of ship reports associated with this last event. The first was the ship Manon (SIWN), located near 13ON 94OW, which reported north-northwest winds of 40 kts at 0600 UTC 28 December. Six hours later, the Manon reported winds of 45 kts as it traversed westward to near 14N 95.5W. At 1800 UTC 28 December, the ship Hansa Stockholm (ELUA3) reported east-northeast winds of 35 kts and 5 m (17 ft) seas while located near 12N 98W.
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