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AGXX40 KNHC 260811
MIMATS

Marine Weather Discussion
NWS National Hurricane Center Miami FL
411 AM EDT Tue Sep 26 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.


...GULF OF MEXICO...

A thermal trough will develop each evening over the NW Yucatan Peninsula, move W-NW across the SW Gulf during the overnight hours and dissipate over the SW Gulf waters by late each morning. Expect the trough to be accompanied by a surge of moderate to locally fresh winds that shift from NE to SE along with possible brief seas to 4 ft through early this morning. Elsewhere, weak high pressure will continue to support mainly gentle E-SE winds and 1-3 ft seas through Wednesday night. The flow increase slightly on Thursday over portions of the western Gulf where mainly moderate NE-E winds are expected along with seas of 3-4 ft. Gentle to moderate NE-E winds are expected elsewhere on Thursday along with seas of 2-3 ft.

The first cold front of the autumn season is depicted by model guidance to move across the northern and western Gulf waters on Thursday, reach a position from northern Florida to the central and SW Gulf waters on Friday, then stall late Friday through Saturday night. Guidance indicates that this front will be rather shallow. The moderate NE-E winds expected over portions of the western Gulf on Thursday will then begin to expand N and S Friday through Saturday night as a result from tightening of the gradient between the front and high pressure that builds southward behind it. Latest guidance from both the GFS and ECMWF agree on this scenario. Seas of about 4-6 ft are expected behind the front mainly over zones GMZ017 and GMZ011, but may be slightly higher if the high pressure behind it becomes stronger. Elsewhere N of the front, winds are expected to be mainly gentle NE-E in direction with seas of 2-3 ft. Winds S and SE of the front are expected to be gentle to moderate SE-S in direction with seas of 2-3 ft. Isolated showers and thunderstorms nay be possible with the front.


...CARIBBEAN SEA AND TROPICAL N ATLANTIC FROM 07N TO 19N BETWEEN 55W AND 64W...

Trades increased across much of the eastern and central Caribbean as central Atlantic ridging builds southwestward towards the eastern Caribbean in the wake of a tropical wave that is currently near 70W. An Ascat pass from 0336Z late last night highlighted mostly gentle to moderate E-SE winds across the basin W of about 70W. The 0154Z Ascat pass from late last night indicated similar winds E of 70W, except for stronger winds in the moderate to fresh range S of about 16N between 69W and 76W. A patch of fresh to strong E winds is S of 15N between 70W and 74W. Seas of 6-8 ft are with the fresh to strong winds. Seas elsewhere E of 70W are in the 4-6 ft range. Seas W of 70W are lower in the 1-3 ft range. Seas of 5-6 ft are over the tropical N Atlantic zones. The trades will expand westward in coverage towards much of the central Caribbean into late Wednesday morning before diminishing on Thursday. E-SE winds of 20-25 kt will continue to pulse across the Gulf of Honduras during the evening and nighttime hours through early Thursday. Seas are forecast to build to 6-7 ft during the period of strongest winds.

The pressure gradient will continue to tighten some across the eastern and central Caribbean Sea, and will begin to tighten across the tropical N Atlantic waters later today as central Atlantic high pressure builds southwestward towards the tropical N Atlantic waters and NE Caribbean Sea in the wake of Hurricane Maria.

Long period NE swell is expected to reach the waters E of the Leeward Islands late tonight and propagate over portions of the eastern tropical N Atlantic zones beginning on Wednesday producing seas to 8 ft. The swell is forecast by wave model guidance to decay on Thursday allowing for these seas to lower below 8 ft.


...SW N ATLANTIC INCLUDING THE BAHAMAS...

Hurricane Maria has moved to just N of the area near 32.6N 73.2W or 200 nm SE of Cape Hatteras North Carolina as of 2 AM EDT. It is moving N or 360 degrees at 6 kt, with maximum sustained winds of 70 kt with gusts to 85 kt. The pressure as of 2 AM EDT is 970 mb. This general motion with some decrease in forward speed is expected through tonight. On the forecast track, the center of Maria will move well E of the southeast coast of the United States during the next couple of days. A recent ASCAT pass E of Maria indicates that the 20-33 kt winds cover the forecast waters N of 27N between 64W and 70W. Both altimeter data and buoy observations reveal that seas 12 ft or greater are occurring to the N of 26N between 65W- 8W. Buoy 41002 at 32N75W is currently reporting seas of 10-18 ft. Even with Maria pulling farther away from the basin through tonight, associated swell will continue to propagate across the forecast waters NE of the Bahamas through most of the forecast period. Wave model guidance suggests that the swell will slowly decay through the end of the week while the bulk of the swell group shifts to the NE portion of the basin.

Of note, Swells generated by Maria are affecting portions of the coast of the southeastern United States and Bermuda and will be increasing along the Mid-Atlantic and southern New England coasts today. Swells also continue to affect Puerto Rico, the northern coast of Hispaniola, the Turks and Caicos Islands, and the Bahamas. These swells are likely to cause life-threatening surf and rip current conditions. Otherwise, in the wake of Maria a surface trough will extend from the N-central forecast waters SW to near the Central Bahamas through Wednesday night then become diffuse Thursday as central Atlantic high pressure builds westward across the eastern portion of the area. Scattered showers and thunderstorms are possible with the trough. On Friday, the ridge is forecast to extend E to W near 26N as a weak cold front approaches the SE United States coast, and far NW waters. Latest model signals suggest that the front will most likely wash out over or very near the far NW waters on Saturday as continental high pressure builds southward and strengthens across it. This will lead to a a gradual increase of NE winds over the NW waters on Saturday along with building seas.

$$


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


.GULF OF MEXICO... None.


.CARIBBEAN SEA AND TROPICAL N ATLANTIC FROM 07N TO 19N BETWEEN 55W AND 64W... None.


.SW N ATLANTIC INCLUDING THE BAHAMAS...
.AMZ113...ATLANTIC FROM 27N TO 31N BETWEEN 70W AND 77W... Tropical Storm Warning N of 29N this morning.



$$

*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.

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