000 AXNT20 KNHC 181805 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 205 PM EDT Tue Apr 18 2017 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 1745 UTC. ...ITCZ/MONSOON TROUGH... The Monsoon Trough axis extends across the western Africa coast near 07N11W and continues to 04N37W to 01N22W. The Intertropical Convergence Zone continues from 01N22W to 00N39W. Scattered moderate/isolated strong convection is within 60 nm north of the axis between 14W-17W, and within 60 nm south of the axis between 17W-21W. Scattered moderate convection is within 60 nm north of the axis between 21W-29W and within 30 nm of the axis between 32W-39W. ...DISCUSSION... ...GULF OF MEXICO... A 1024 mb high is centered over the western Atlantic near 29N67W with a surface ridge extending across northern Florida to the northern Gulf of Mexico along 29N. A surface trough, identified very well in the surface isobaric pattern and in satellite imagery, extends from near 29N83W to 23N85W. The combination of this trough and a shortwave trough swinging eastward over the eastern Gulf is resulting in ample deep atmospheric moisture and instability over that portion of the Gulf. Both satellite and radar imagery shows scattered to numerous showers and thunderstorms from 24N to 26N east of 85W to just west of the Florida Keys and southwest Florida. This activity is capable of producing strong gusty winds as it shifts generally towards the northwest. Gentle to moderate east to southeast flow is noted elsewhere across the basin. A rather vigorous mid to upper level trough is observed on water vapor imagery to be moving through eastern Texas. A surface trough is along and just inland the Texas coast. Very deep moisture ahead of the troughs and divergence aloft is supporting a an almost solid line of scattered moderate to isolated strong convection over the far northwest waters north of 26N between 94W and just inland the Texas coast north of Galveston. Weakening scattered moderate convection is to the south within 30 nm either side of line from 26N95W to 24N96W to 21N96.5W. This activity is expected to continue on weakening through this afternoon and evening as drier air is advected in behind it. The surface high pressure ridge is forecast to weaken some on Wednesday. CARIBBEAN SEA... Upper level disturbances ridging along in strong southwest to west flow associated with a jet stream branch that rounds the base of a sharp mid/upper level trough over eastern Texas are combining with ample moisture and instability along with low level moist easterly flow resulting in an increasing area of scattered moderate/isolated strong convection from 16N to 21N between 80W and the coast to Belize and the Yucatan Peninsula. Scattered showers and isolated thunderstorms are seen elsewhere west of 78W. This activity will continue to increase and expand in coverage through afternoon and evening, and gradually shift eastward through Thursday as the tough axis migrates eastward to the eastern Gulf of Mexico. Another upper level disturbance aloft riding eastward in westerly flow has enhanced scattered shower and thunderstorm activity over the northern eastern Caribbean Sea within 30 nm of line from 16N69W to 17N66W. Isolated showers and thunderstorms are observed elsewhere east of 71W. The upper atmospheric pattern with disturbances riding in the westerly flow in combination with plenty of moisture and instability favors the eastern Caribbean and majority of Lesser Antilles and also Puerto to be quite active with scattered to possibly numerous at times showers and thunderstorms through Friday. Northeast winds will increase to strong category at night near and through the Windward Passage Wednesday and Thursday. ...HISPANIOLA... High level clouds are seen streaming eastward over Hispaniola, however, for the most part they are rather thin allowing for daytime heating to filter through these clouds. This in combination with plenty of atmospheric instability is allowing for isolated showers and thunderstorms to develop over the interior of the island, and over the southwest section of Haiti. Similar activity is over the nearby waters. The trend appears for additional moisture and instability to exist over and near Hispaniola through Friday. This is expected to set off additional shower and thunderstorm activity, especially if there are breaks in the presently observed upper clouds to allow for more heating would help provide further impetus for the development of additional activity. Some of the shower and thunderstorm may bring locally heavy rainfall to some locations. ATLANTIC OCEAN... A 1024 mb high is centered over the western Atlantic near 29N67W. To the east, a deep low of 994 mb is centered at 32N44W with strong to near gale force winds to its north and south to near 27N between 41W and 52W with seas of 13 to 17 ft. A trough, formerly a cold front, is to its east from near 32N36W to 23N34W to 18N44W. Another surface trough extends from the low 29N45W and northwest to 30N48W. Scattered showers and thunderstorms are noted north of 27N between 39W and 46W. The low is forecast to move east during the next 24 hours, reaching near 32N42W with pressure of 998 mb and associated strong to near gale force winds north of 31N between 35W and 40W. By Thursday, the low is forecast to track to north of the area near 34N39W with a pressure of 995 mb, with gale force winds over its northeast semicircle. Scattered showers and isolated thunderstorms south of 27N and west of 70W will change little through Thursday as mid/upper level troughing stays west of the basin with upper level disturbances moving eastward ahead of it to the area of the Bahamas and to near 70W. The 1024 mb high is forecast to dissipate Wednesday. Little change is expected elsewhere. For additional information please visit http://www.hurricanes.gov/marine $$ Aguirre