AGXX40 KNHC 221948

Marine Weather Discussion
NWS National Hurricane Center Miami FL
248 PM EST Wed Nov 22 2017

Marine Weather Discussion for the Gulf of Mexico, Caribbean Sea, and Tropical North Atlantic from 07N to 19N between 55W and 64W and the Southwest North Atlantic including the Bahamas


A rather complex weather pattern continues over the gulf waters. The latest surface analysis reveals A 1013 mb low over the NE gulf near 28N85W with a cold front extending southwestward to a 1012 mb low at 26N88W. A trough extends from the 1012 mb low to 24N88W and continues southwestward to the SW gulf at 20N95W. Behind these features, a cold front extends from Panama City southwestward to 27N90W, to 26N94W to 23N96W and to inland Mexico just north of Tampico. A vigorous short-wave trough rotating through a very well pronounced longwave trough that stretches from the NE U.S. southwestward to a cyclonic circulation diving SSE over the NW Gulf at 26N95W, and continuing southwestward to across southeastern Mexico and to eastern Pacific Ocean is supporting these features that consist of of the complex weather pattern. Strong high pressure is build southward over the western gulf behind the front cold front. A very tight pressure gradient between the high pressure and the cold front has resulted in a large swath of strong to gale force northerly winds overtaking the waters to the W of the cold front. A swath of NW gale force winds has slipped southward within about 60-70 nm off the Mexican coast ahead of the cold front to just northwest of the southern end of the trough. This was nicely exhibited in the Ascat pass from this morning.

Doppler Radar shows scattered showers and thunderstorms advancing rapidly northeastward over the NE gulf waters. Latest satellite imagery shows clusters of scattered showers and thunderstorms over much of the gulf to the SE of a line from southeastern Louisiana to 25N96W and to 19N96W. The activity over the western gulf behind the front is being mainly sustained by instability aloft generated by the cyclonic circulation at 26N95W.

As for the forecast, the low near 28N85W will lose its identity through Friday while the one near 26N88W slowly tracks east- northeastward to the far eastern gulf waters through early on Friday before moving inland central Florida Friday afternoon pushing the cold front to the far SE waters by late Saturday as it weakens.

Wave model guidance suggests that combined seas will peak to a maximum of around 14 ft in association with the gale force conditions tonight before subsiding to around 10 ft early Thursday night and to less than 8 ft early on Friday as high pressure settles back over the entire area. The related pressure gradient will bring generally moderate to fresh northerly flow through Friday night and light to gentle northerly flow Saturday through Sunday night, except for light anticyclonic flow over the central gulf on Saturday and over the NW gulf on Sunday. Seas will lower to 2-3 ft over the entire waters on Saturday, except for the SE part of the gulf where seas will be slighter higher in the 3-4 ft range due to a NW swell. These 3-4 ft seas will subside to 2-3 ft during Sunday morning.


A persistent surface trough is analyzed along 81W/82W from 11N to 21N. Scattered showers and isolated thunderstorms are seen within 60 nm W of the trough from 11N to 14N, while isolated showers and thunderstorms are elsewhere within 120 nm of the trough. Latest moisture convergence model guidance indicates that the trough will linger over the west-central Caribbean through at least Friday. Scatterometer data detected a NE to SE wind shift of mainly gentle winds across the trough axis, with the exception of moderate northerly winds just off the coast of Nicaragua. Moderate to locally fresh easterly winds are noted over the eastern Caribbean, with mainly fresh winds off the coast of Venezuela, including also the ABC Islands. Winds will diminish over the S central and SE portion late this week as high pressure N of the area weakens in response to the developing low pressure along the east coast of the U.S. Seas will be quite low, in the 2-4 ft range for the next few days. The weak pressure gradient should remain in place over the Caribbean until Thursday, when a cold front will enter the NW Caribbean from the Gulf of Mexico. Model guidance indicates that the front will then stall and weaken over the NW Caribbean Friday. The pressure gradient between building high pressure over Central America and the frontal boundary should bring an increase in northerly winds of mostly 20 kt with possible pockets of 25 kt within about 120 nm off the Nicaragua coast Thursday night through Monday night along with max combined seas of 6 or 7 ft. There is a possibility that seas may reach 8 ft on Monday as suggest by the latest run of the TAFB NWPS model output.


A ridge is now confined to the extreme NE waters. Interestingly, a low has formed at 29N70W with a forming cold front extending southwestward to the central Bahamas, and a developing warm front that stretches southeastward to near 25N63W. The cold front that was analyzed this morning over the NW portion of the area has become diffused. The low is forecast to attain a fast northeast motion later this afternoon and evening as deep troughing to the W of the area progresses eastward. Latest satellite imagery shows a large area of scattered moderate to strong convection moving quickly eastward within 90 to 240 nm to the E of the low. Models have been consistently noting that a very tight pressure gradient will set up to the E and SE of the low beginning this evening. This is expected to occur as the low moves across the eastern part of zone AMZ115 near 29N67W early tonight. So a gale warning was issued this morning within 150 nm of the low in its southeastern semicircle where seas are forecast to build to a maximum of about 14 ft. The low rapidly deepen as it moves to just N of the forecast waters near 32N66W by early on Thursday with a pressure of 1001 mb. The associated cold front will extend from the low to 26N67W where it becomes stationary to near eastern Cuba. The gale force southerly winds are expected to be N of about 28N and E of 67W at that time, with seas of 8-11 ft. These conditions will exit zone AMZ115 during Thursday afternoon.

Another low pressure system, currently over the eastern Gulf of Mexico, will move across Florida and into the far NW waters by late Friday morning. The associated cold front will move across the western and central waters trough early Sunday morning, and across the eastern and SE waters late Sunday through Monday as it weakens to a frontal trough. Widespread showers and thunderstorms with possible gusty winds are expected with both the low and the cold front. Model guidance suggests that another cold front will move across the NW portion on Saturday and across the remainder of the waters into Monday followed by a large dome of strong continental high pressure. Will have to watch as to how future model guidance depicts the northerly winds behind this next front as latest model suite is differing with respect to this.


.WARNINGS...Any changes impacting coastal NWS offices will be coordinated through AWIPS II Collaboration Chat, or by telephone:

.GMZ011...NW GULF INCLUDING STETSON BANK... Gale Warning today for frequent gusts.
.GMZ017...W CENTRAL GULF FROM 22N TO 26N W OF 94W... Gale Warning today W of 96W.
.GMZ023...SW GULF S OF 22N W OF 94W... Gale Warning today into Thu.


.SW N ATLANTIC INCLUDING THE BAHAMAS... AMZ115...N of 28N E of 67W through early Fri.


*For detailed zone descriptions, please visit: http://www.nhc.noaa.gov/abouttafbprod.shtml#OWF

Note: gridded marine forecasts are available in the National Digital Forecast Database (NDFD) at: http://www.nhc.noaa.gov/marine/grids.php

For additional information, please visit: http://www.nhc.noaa.gov/marine


.Forecaster Aguirre. National Hurricane Center.