000 AGXX40 KNHC 280800 MIMATS Marine Weather Discussion NWS National Hurricane Center Miami FL 400 AM EDT Thu Sep 28 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 in the NW Yucatan Peninsula, move W-NW across the SW Gulf during the overnight hours and dissipate in 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 seas possibly briefly reaching to 4 ft. The 0350Z Ascat pass from last night indicated such winds. After a long period of weak high pressure supporting gentle E-SE winds and 1-3 ft seas, the NE to E flow will increase slightly today 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 along with seas of 2-3 ft. Upcoming near term and long term changes are as follow: The first cold front of the autumn season will move across the northern and western Gulf waters tonight, reach a position from northern Florida to the central and SW Gulf waters on Friday, then stall along a position from near Tampa Bay to the far western Gulf by Friday evening and gradually become diffuse through the weekend as strengthening high pressure builds southward across the area. Moderate NE-E winds across parts of the western Gulf will begin to expand N and S Friday through Saturday night as a result of the tightening of the gradient between the dissipating front and the high pressure that builds southward across it. The resulting tight pressure gradient is forecast to induce NE-E winds of fresh to strong intensity over the NE Gulf beginning Saturday night. These winds then will expand westward to S of southeastern Louisiana on Sunday. The southern extent of these winds should reach near 27N. Seas resulting from these winds should build to around 8 ft by Sunday night, but should be confined to primarily the coastal waters zones. Elsewhere N of the front winds will be mainly in the gentle range from the NE-E in direction through tonight, with seas of 2-3 ft. These winds will gradually increase to the moderate range through Sunday night, with seas building to 4-5 ft. NW-N winds of about 20-25 kt are expected within about 60 nm of the coast of Mexico from 19N-20N from Saturday morning through Monday as the areal coverage diminishes. Winds S and SE of the front are expected to be gentle to moderate E-SE in direction with seas of 2-3 ft. Scattered showers and isolated thunderstorms are possible with the front. An area of low pressure is expected to develop to the E of central Florida on Friday, then move in a general SW to SW to W direction during the weekend while weakening to a trough as it moves across the eastern Gulf Sunday night through Monday night. The combination of this feature and the aforementioned strengthening high pressure over the NE Gulf will further help to sustain the strong NE winds that are forecast to develop over that portion of the Gulf on Saturday night. Scattered to numerous showers and thunderstorms are possible with the trough. ...CARIBBEAN SEA AND TROPICAL N ATLANTIC FROM 07N TO 19N BETWEEN 55W AND 64W... A recent Windsat pass indicated fresh to strong E winds S of 16N between 70W and 75W. Seas of 6-8 ft accompany these winds. Seas elsewhere are in the 4-6 ft range, except for slightly lower seas of 3-5 ft in the NW part of the Caribbean Sea. Seas in the tropical N Atlantic zones have built to the range of 6-8 ft due to a long period NE swell propagating through those waters. The fresh to strong trades will diminish to mainly fresh trades by this evening, with seas lowering to just under 8 ft. The strong E-SE winds that were occurring yesterday across the Gulf of Honduras have diminished to the gentle to moderate category. The southern extent of an upper level trough located over the eastern Gulf of Mexico reaches S to the NW Caribbean. Meanwhile, a tropical wave is analyzed just E of the Yucatan Peninsula and S to inland Central America. The availability of ample moisture and instability that is present over the western Caribbean and that is being worked on by the upper trough along with tropical wave energy has resulted in scattered shower and thunderstorm activity over much of the NW Caribbean N of 19N. This activity will linger through the next few days while increasing in coverage as the wave moves inland the Yucatan Peninsula and becomes involved in a large cyclonic gyre that is forecast ton set up over the Yucatan Peninsula and the northern portions of Central America, and including the far western Caribbean. Moisture related with the ongoing convection over the NW Caribbean will continue to advect N-NE under upper level southerly wind flow, that exists to the E of the upper level trough. This moisture is forecast to lead to increasing chances for scattered to numerous showers and thunderstorms over the NW and N-central Caribbean and including the Yucatan channel and vicinity waters during the next few days. Some of this activity is capable of producing gusty winds and frequent lightning at times. ...SW N ATLANTIC INCLUDING THE BAHAMAS... Swell produced by Tropical Storm Maria, presently well N of the area will continue to propagate through the forecast waters NE of the Bahamas through Friday night while slowly decaying. A surface trough that is in the wake of Maria will extend from the N central forecast waters SW to near the Central Bahamas through Thursday night, then dissipate Friday as central Atlantic high pressure builds westward across the eastern part 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 moves over the far NW waters. Model guidance suggests that the front will stall from near 31N65W to the NW Bahamas on Saturday with a surface low forecast to develop along the front near 28N79W. The low will move northeastward to N of the forecast waters along the dissipating front Saturday night into Sunday, while another low that develops to the E of central Florida on Friday tracks to in the general direction of SW to SW to W across central Florida and towards the eastern Gulf of Mexico through Sunday. Strong high pressure will surge southward over the NW waters behind the stalled and weakening front. The associated tight pressure gradient is expected to bring strong to near gale force NE winds across the waters W of a line from near 31N75W to 28N80W on Sunday along with building seas. The gradient is expected to slacken just enough on Monday to allow for these winds to diminish to the fresh to locally strong category on Monday. Seas produced by these winds will then lower to below 8 ft by late on Monday. $$ .WARNINGS...Any changes impacting coastal NWS offices will be coordinated through AWIPS II Collaboration Chat, or by telephone: .GULF OF MEXICO... None. .CARIBBEAN SEA AND TROPICAL N ATLANTIC FROM 07N TO 19N BETWEEN 55W AND 64W... None. .SW N ATLANTIC INCLUDING THE BAHAMAS... None. $$ *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.