000 AGXX40 KNHC 120800 MIMATS Marine Weather Discussion NWS National Hurricane Center Miami FL 400 AM EDT Sat Aug 12 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... The main feature continues to be a high pressure of 1018 mb centered over the central Gulf waters at 26N88W. The associated anticyclonic flow consists of light to gentle winds over the basin, with the exception of the eastern portion of the Bay of Campeche where there northeast to east moderate winds are present due to the tighter gradient with the Yucatan Peninsula thermal trough that has moved to just offshore that peninsula. A partial Ascat pass from 0230Z depicted these winds. The buoys are reporting seas in the 1-3 ft range E of 94W, and 3-4 ft seas W of 94W. Scattered showers and isolated thunderstorms are noted over the portions of the far eastern Gulf. Most of this activity was inland the Florida peninsula yesterday and last night induced by a surface trough that combined with the already present warm and moist unstable air mass, and has since moved offshore. Latest trends observed on radar and satellite imagery indicate that it is weakening as it moves across the far eastern boundary of the E Gulf offshore waters. Similar activity moving quickly to the west is noted over the Bay of Campeche between 92W and 96W. This activity is weakening as well. For this forecast, little overall changes will be expected with regards to winds and seas through the period as the western extension of the Atlantic sub-tropical ridge will extend westward to roughly near 28N. Intermittent high pressure cells will form along the ridge over the eastern Gulf during this forecast period. The trough over the Florida peninsula will remain in place through Monday. Related similar shower and thunderstorm activity, as mentioned above, are expected to move into the far eastern Gulf during the evenings and at night. ...CARIBBEAN SEA AND TROPICAL N ATLANTIC FROM 07N TO 19N BETWEEN 55W AND 64W... Latest Buoy and available scatterometer data show generally gentle to moderate NE to E trades throughout, except for stronger trades of fresh to strong intensity confined to the far south- central waters S of about 12.5N and between 69W and 71W. The buoys and latest altimeter data indicate seas in the range of 4-6 ft, except for lower seas of 3-4 ft over the western Caribbean, and seas of 2-3 ft in the far NE part of the sea. A tropical wave is analyzed near 76W S of 21N at 06Z moving westward at 10-15 kt. This wave will move across the rest of the central Caribbean through tonight, and the western Caribbean through Sunday night before it moves inland central America late Sunday night or early on Monday. A large and well-defined tropical wave currently over the central Atlantic along 44W/45W S of 20N is expected to begin to move across the eastern portion of the Tropical N Atlantic waters on Sunday evening, and move across the rest of those waters through early Monday evening. In its wake, the gradient will tighten ahead of yet another large tropical wave expected to approach 55W on Tuesday. Trades will increase behind the first wave Monday night into Tuesday, and continue to increase on Tuesday in advance of the second wave. These winds are forecast to reach fresh to strong intensity over the Tropical N Atlantic waters mainly N of 15N Tuesday night into Wednesday, with seas building to 8-9 ft there. The fresh to strong trades over the far south-central waters are forecast to shrink in coverage this afternoon, then re-develop late this afternoon and evening and continue through tonight before diminishing on Sunday afternoon. Model guidance indicates that these winds will pulse again to fresh to strong S of 13N between 70W-75W Sunday night, and expand N to near 15N and W to near 77W by late Sunday night. This cycle of the winds diminishing in the afternoons and pulsing back up in the late afternoons and evenings will repeat itself through the middle of next week, at which time the passage of the aforementioned tropical wave, currently along 44W/45W, will aid sustaining a tight gradient inducing fresh to strong trades across much of the central and eastern Caribbean. Scattered moderate to strong thunderstorms are active along the monsoon trough north of Panama and southern Costa Rica due to speed convergence. This activity should remain quite active through early next week. ...SW N ATLANTIC INCLUDING THE BAHAMAS... High pressure is present over the basin, with the exception of a broad area of low pressure that is located near new, with a trough S SW to near the NE tip of the Dominican Republic. Latest satellite imagery shows scattered showers and thunderstorms between 90 and 240 nm to the NE of the low, and within 100 nm N of the low. Seas are in the range of 4-6 ft N and E of the Bahamas, except for higher seas of 6-8 ft associated with a tight gradient between the low and high pressure to its N and NE. This gradient is producing strong E to SE winds from 22N to 25N between 64W- 68W, with seas of 6-8 ft. Low seas in the range of 1-2 ft are W of the Bahamas, including the Straits of Florida. The main issue over the next few days with respect to possible significant impacts to winds and seas over some portions of the basin will be attributed to the area of broad low pressure. This system is forecast to track to the NW through early Sunday, then track N NE through early next week as it recurves to the E of the Bahamas as suggested by consensus of the global models. Atmospheric conditions are forecast to become a little more favorable for the low pressure system to acquire tropical cyclone characteristics through early next week per latest NHC outlook. The sub-tropical Atlantic ridge will then re-build westward near 27N beginning on Monday, with the associated gradient expected to support gentle to moderate winds E to SE winds south of the ridge and gentle to moderate S to SW winds N of the ridge. E winds will pulse to fresh to strong between the SE Bahamas and Hispaniola in the afternoons and at night beginning on Monday night. In response to an approaching large tropical wave, NE winds are forecast to increase to fresh to locally strong intensity over zone AMZ127 beginning late Tuesday afternoon or evening along with seas to build up to around 8 ft. $$ .WARNINGS...Any changes impacting coastal NWS offices will be coordinated through AWIPS II Collaboration Chat, or by telephone: .GULF OF MEXICO... None. .CARIBBEAN SEA AND TROPICAL N ATLANTIC FROM 07N TO 19N BETWEEN 55W AND 64W... None. .SW N ATLANTIC INCLUDING THE BAHAMAS... None. $$ *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.