000 AXNT20 KNHC 210014 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 814 PM EDT Thu Apr 20 2017 ...Correction to include Atlantic Gale Warning 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 1800 UTC surface analysis and satellite imagery through 2345 UTC. ...SPECIAL FEATURES... Tropical Depression ONE became Tropical Storm Arlene at 20/2100 UTC. The center of T.S. Arlene is near 37.7N 42.0W and is moving west-northwest, or 290 degrees at 22 knots. The estimated minimum central pressure is 993 mb. The maximum sustained wind speeds is 40 knots with gusts to 50 knots. Numerous moderate convection is SW of the storm center from 37N to 39N between 41W and 45W. Please read the public advisory under the WMO header WTNT31 KNHC and under the AWIPS header MIATCPAT1. A tight pressure gradient between a broad low pressure system centered SW of T.S. Arlene and high pressure to the W will support gale force winds N of 30N between 49W and 54W starting early Saturday morning and continuing to the evening hours. Please see the latest National Hurricane Center High Seas forecast under the WMO header FZNT02 KNHC and under the AWIPS header MIAHSFAT2 for further details. ...ITCZ/MONSOON TROUGH... The Monsoon Trough extends across the western Africa coast from 07N12W to 03N19W. The Intertropical Convergence Zone continues from 03N19W to 02N33W to the coast of Brazil near 02S43W. Scattered moderate convection is from 03S to 10N between 20W and 31W. Isolated showers and tstms are from 0N to 05N E of 20W. ...DISCUSSION... GULF OF MEXICO... A middle to upper level low centered NW of the Yucatan Peninsula covers the western Gulf of Mexico where water vapor imagery show very dry air aloft, which supports in part fair weather conditions there. However, middle to upper level ridging across the western Caribbean allows for a diffluent wind pattern over the SE Gulf where abundant moisture support numerous moderate convection and isolated tstms as indicated by the GOES lighting density product. This convection is located S of 26N E of 89W ahead of a surface trough in the NW Caribbean that will move over the Yucatan Peninsula tonight bringing heavy showers to the region. The trough is forecast to become a center of low pressure Saturday morning over SE waters and then will track over NE Gulf waters Sunday where it will dissipate. Otherwise, surface ridging dominates the northern Gulf waters being anchored by a 1019 mb high near 29N84W. This is providing mainly E-SE light to moderate flow across the basin, except in the SE Gulf where the gradient tightens due to the approaching surface trough and supports fresh NE winds. CARIBBEAN SEA... The main feature in the Caribbean is a surface trough in the NW basin from 22N82W to central Honduras. This elongated area of low pressure is located under a broad area of middle to upper level diffluent flow that along with abundant moisture in the region support scattered heavy showers and isolated tstms N of 14N W of 77W. This shower activity will continue overnight as the trough continues to move west towards the Yucatan Peninsula. Latest scatterometer data show fresh to locally strong E-NE winds in the vicinity of the trough. Fresh winds extends to the central Caribbean N of 15N, including the Windward Passage. Moderate trades dominate elsewhere. Otherwise, SW flow aloft continue to bring moisture from S America and the EPAC to the NE Caribbean, thus supporting cloudiness in the region with possible isolated showers. ...HISPANIOLA... Broken to overcast skies continue across the Island with possible isolated showers extending to adjacent waters. This is due to abundant low level moisture and a middle diffluent wind pattern west of the Island and also moisture advection by SW flow in the upper levels. These conditions are expected to continue during the next two days. ATLANTIC OCEAN... Tropical storm Arlene is over central Atlantic waters N of the area. See the special features section for further details. A cold front enters the area from 30N42W to 23N52W then dissipates to 28N75W. No convection is associated with it. Surface high pressure dominate elsewhere. Arlene is forecast to dissipate in 24 hours. However, gale-force winds will develop over the central Atlantic Sat morning. For additional information please visit http://www.hurricanes.gov/marine $$ Ramos