000 AXNT20 KNHC 181149 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 649 AM EST Sun Feb 18 2018 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 0600 UTC surface analysis and satellite imagery through 1145 UTC. ...SPECIAL FEATURES... Caribbean Sea Gale Warning: A tight surface pressure gradient continues between a surface high pressure in the western Atlantic and lower surface pressure in northern sections of South America. This pattern supports winds pulsing to minimal gale force near the coast of Colombia through early next week. The resultant wave heights with the gale-force winds will range between 12-16 ft. Please read the latest NHC High Seas Forecast under AWIPS/WMO headers MIAHSFAT2/FZNT02 KNHC for more details. ...MONSOON TROUGH/ITCZ... The monsoon trough axis extends from the southern coastal sections of Liberia near 05N08W southwestward dipping to below the Equator at 18W as the ITCZ axis to 03S27W and to the coast of Brazil near 04S38W. Scattered moderate isolated convection is within 60 nm S of the ITCZ axis between 24W and 28W. Similar convection is just to the N of the Equator within 30 nm of line from 01N27W to 02N31W to 02N34W. ...DISCUSSION... GULF OF MEXICO... A surface ridge extends from an Atlantic Ocean 1026 mb high pressure center located near 28N64W, to across central Florida, to a 1023 mb nearly stationary high centered at 27N83W and continues west-northwestward to the NW Gulf near 28N94W. A weak surface trough is analyzed over the NE Gulf from near Apalachicola to 28N87W to 27N89W. Isolated weak showers are possible along the trough. Similar showers are over the extreme southeastern gulf near NW Cuba. The ridge will continue to maintain mainly gentle to moderate southeast winds in the western Gulf, and light to gentle east to southeast elsewhere through Sun night with the exception of moderate winds over the SE waters and the Straits of Florida. Areas of dense fog producing reduced visibility to below 1 nm are again expected through this morning mainly N of 27N, persisting into this afternoon over some locations. Isolated showers are over some portions of the eastern gulf and far SE waters near the Straits of Florida. Expect increasing winds and building seas by early next week as high pressure strengthens in the western Atlantic Ocean. A thermal trough will develop over the western Yucatan Peninsula during each afternoon. The trough will drift westward across the eastern Bay of Campeche during the overnight hours, and then dissipate in the SW Gulf waters by late each morning. CARIBBEAN SEA... Please read the SPECIAL FEATURES section for details regarding the Gale Warning near the coast of Colombia. Patches of broken to at times overcast low clouds with isolated showers are quickly moving westward across the western and central Caribbean N of about 14N, including waters adjacent to the southwest tip of Haiti and waters just east and west of Jamaica. Similar clouds with brief passing isolated showers are noted over portions of the eastern Caribbean. Over the eastern Caribbean, the moisture coverage has decreased since yesterday as very dry air aloft has moved into that portion of the sea. A tight pressure gradient between a high pressure system that is in the western Atlantic Ocean, and lower pressure in northern sections of South America, will continue to support pulsing winds of minimal gale force near the coast of Colombia through early next week. Fresh to locally strong trade winds are expected elsewhere across the Caribbean Sea. The high pressure will be reinforced by a stronger high pressure system on Mon. The stronger system will bring increasing winds and building seas across the eastern and central Caribbean Sea, and the Tropical N Atlantic waters possibly into the middle of next week. ATLANTIC OCEAN... A central Atlantic upper level trough enters the area through 32N25W, and stretches southwestward to an elongated cyclonic circulation that is dropping southward near 24N43W, and continues southwestward to 15N51W where it becomes a cyclonic shear axis westward to 14N58W and to the eastern Caribbean Sea near 14N66W. A surface trough extends from 31N50W to 26N58W, and another one extends from near 29N43W to 24N44W to 19N44W. Isolated showers and thunderstorms are noted within 240 nm to the E of the second trough, and within 60 nm W of the same trough from 20N to 23N. Isolated showers are near the first trough. Other than these troughs, the Atlantic is dominated by high pressure as a nearly 1026 mb high center is near 28N64.5W, and another 1026 mb high center is over the eastern Atlantic near 29N38W. A ridge extends from the 1026 mb high at 28N64.5W westward to across central Florida. In the upper levels, an anticyclone is near 22N66W, with its broad anticyclonic flow covering just about the entire western half of the area. An upper level trough has entered the far NW corner of the area. Subsidence and dry air aloft associated with the upper anticyclone is suppressing any deep convection from developing. The upper trough is void of any shower activity as it nudges into a very stable atmospheric environment. Isolated showers are seen over the waters between Andros Island and the Straits of Florida. The aforementioned high pressure ridge will retreat eastward today allowing for a weak cold front to move off the southeastern United States coast. The front will quickly become stationary and dissipate across the northwest portion on Mon. Gentle to moderate south to southwest winds will prevail to the north of the ridge, with moderate to fresh winds expected generally to the south of 25N, except becoming strong along the north coast of Hispaniola and the northern approach to the Windward Passage each evening. The ridge will be reinforced by a stronger high pressure system on Mon through Tue. Over the eastern portion of the Atlantic, extensive mid and upper level moisture in the form of overcast to broken mid and high level clouds are observed streaming northeastward from northeastern S America to within 300 nm either side of a line from 05N51W to 13N37W to 17N28W to 18N23W where the moisture thins out allowing for the clouds to transition to mainly scattered high clouds to inland the coast of Africa at 19N16W. This area of moisture and clouds are driven by a rather strong jet stream branch that is along the southeast sector of the upper level trough described above. Scattered moderate convection is along and just inland the coast of S America between 43W-47W. Isolated showers are possible elsewhere from 02N-11N between 41W-51W, and also from 10N-19N between 30W-41W. For additional information please visit http://www.hurricanes.gov/marine $$ JA/ERA