000 AXNT20 KNHC 211910 AAA TWDAT Tropical Weather Discussion...Updated NWS National Hurricane Center Miami FL 210 PM EST Tue Feb 21 2017 Updated to include new conevction under ITCZ/Monsoon Trough Tropical Weather Discussion for North America, Central America Gulf of Mexico, Caribbean Sea, northern sections of South America, and Atlantic Ocean to the African coast from the Equator to 32N. The following information is based on satellite imagery, weather observations, radar and meteorological analysis. Based on 1200 UTC surface analysis and satellite imagery through 1830 UTC. ...SPECIAL FEATURES... A 1010 mb surface low associated with an anomalously south deep layer low is near 24N63W. A cold front extends from the low southwestward to the northeast portion of the Caribbean Sea. These features are within a broad area of low pressure over the central Atlantic present north of 19N between 50W and 71W. A second cold front enters the area through 32N59W, and continues to 27N70W. This cold front will merge with the cold front that extends from the low by this evening as the low continues moving southeastward while weakening. The merged cold front is forecast to be along a position from near 32N53W to 16N61W this evening. A very tight pressure gradient will become established between the front and strong high pressure to its east. This will induce near gale to gale force south to southwest north of 27N within 240 nm east of the merged front. The gale force winds are expected to lift north of the discussion by Wednesday night. See latest NWS High Seas Forecast under AWIPS/WMO headers MIAHSFAT2/FZNT02 KNHC for more details. ...ITCZ/MONSOON TROUGH... The Monsoon Trough extends from the African coast near 08N13W to 04N18W. The Intertropical Convergence Zone axis extends from 04N18W to the Equator near 27W and along the Equator to 38W. Scattered moderate convection is within 60 nm of the axis between 14W and 18W. Scattered moderate is observed north of the ITCZ within 60 nm of a line from 03N30W to 03N36W. An increasing area of scattered moderate/isolated strong convection is noted from 01N to 06N west of 45W to the coast of South America. ...DISCUSSION... GULF OF MEXICO... Water vapor imagery shows a deep layer low centered over southern Arkansas extending into northern Louisiana. A deep layer trough extends from the low over the central Gulf waters and to the eastern Bay of Campeche. The troughing supports a 1008 mb low centered over northwest Mississippi, with a cold front dropping south-southwest from the low to 30N88W to 25N91W to just southeast of Veracruz Mexico. A post-frontal trough enters the northwest portion from near Galveston to near 27N95W. A squall line is just ahead of the cold front north of 27N. Scattered thunderstorms, increasing with time, are along and within 60 nm east of the squall line. Scattered showers and isolated tstms are seen elsewhere along and east of the cold front north of 27N. Strong middle to upper level diffluence occurring east of the deep layer trough is helping to enhance this activity. Scattered showers are elsewhere along and within 60 nm east of the front, and within 120 nm northwest of the front. Otherwise...the eastern half of the basin is under the influence of surface ridging that stretches from the NE United States southwestward to that portion of the basin. Latest satellite imagery is showing extensive middle to upper level cloudiness streaming eastward ahead of the aforementioned deep layer tough and cold front to across just about the entire Florida peninsula. Mostly clear skies are behind the cold front where water vapor imagery shows very dry conditions under strong strong subsidence present there. The exception is in the northwest portion of the Gulf where scattered showers and thunderstorms have developed within 60 nm east of the post-frontal trough. Looking ahead...the cold front is forecast to move into the eastern Gulf by tonight as the post-frontal trough merges with it. The merged front is forecast to reach a position from the eastern section of Florida panhandle to the Yucatan Channel tonight as a surface low forms along the front near 28N85W. The low will move southeastward on Wednesday, and move across the Florida peninsula near 27N pushing the front through the Straits of Florida late on Friday. Strong northwest winds behind the front will diminish to moderate northeast through Thursday as high pressure in the wake of the front weakens. CARIBBEAN SEA... Overall the Caribbean basin continue under fairly tranquil conditions this afternoon, with the exception of the northeastern waters. There an area of low pressure N-NE of Puerto Rico centered near 24N63W extends a cold front rather far to the southwest to just south of Antigua, to over Montserrat and to near 16N71W. Low level moisture convergence within southerly winds focused along a surface trough analyzed from Saint Martin south- southwest to near 12N65W is generating widely scattered showers and isolated thunderstorms north of 15N east of the trough. This activity will gradually shift east of the basin through tonight as the trough is forced eastward in response to the cold front pushing south-southeast. Otherwise...dry and stable air aloft coupled with gentle to moderate east to northeast winds are prevailing and expected to persist through tonight, except in the northwest portion of where a cold front currently moving through the central Gulf of Mexico will make its entrance. The cold front will reach from central Cuba to he northeast side of Nicaragua Wednesday night, then become stationary from eastern Cuba to northeast Nicaragua late on Thursday. Strong northwest flow will briefly follow in behind the front on Wednesday before diminishing to fresh west to northwest winds on Thursday. ...HISPANIOLA... Scattered to locally broken low clouds with possible developing isolated showers are observed along and just inland much of the northern coast of the island, and over much of the northwest corner of Haiti. Patches of low-level moisture moving southward due to northerly flow to the west of the Atlantic low pressure system and cold front will approach the north coast of the island today and tonight providing for chances of precipitation. Any shower activity that approaches the north coast will be moving rather quickly to the south. ATLANTIC OCEAN... A broad area of low pressure is noted across the SW North Atlc focused on a 1010 mb low centered near 24N63W. The associated cold front extends southwestward to the northern Caribbean Sea. Abundant deep layer moisture is evident to the east of the low and cold front as it is being supported by a very pronounced sharp deep layer trough that enters the area through 32N60W, and continues southward to the deep layer low at middle/upper level low at 21N60W. The instability present east of the trough in conjunction with the deep layer moisture is producing scattered showers and thunderstorms north of 17N between 50W and 61W. The low and its associated cold front is forecast to continue moving eastward and merge with another cold front that extends from 32N59W to 27N70W as of 12Z. The entire system will move further eastward over the central Atlantic by Wednesday producing the Special Features near gale to gale force conditions mentioned above. New low pressure will move from the Gulf of Mexico northeastward to near 27N80W by Thursday morning, with a trailing cold front. Strong to near gale east-southeast winds are expected east of the low to near 71W. Otherwise...the remainder of the SW North Atlc is under the influence of a surface ridge anchored by a 1032 mb high centered over New England. The ridge will slide offshore through Wednesday. Finally...the remainder of the eastern Atlc is under the influence of another surface ridge anchored by a 1031 mb high centered to the northeats of the Azores near 44W19W. The ridge axis extends southwestward from the high to 32N31N to 17N43W. For additional information please visit http://www.hurricanes.gov/marine $$ Aguirre