000 AXNT20 KNHC 132356 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 755 PM EDT Sun Aug 13 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 1800 UTC surface analysis and satellite imagery through 2315 UTC. ...SPECIAL FEATURES... Tropical Storm Gert is centered near 28.1N 71.7W at 13/2100 UTC, or about 438 nm WSW of Bermuda moving toward the north-northwest, or 335 degrees, at 9 kt. A turn toward the north is forecast to occur tonight, followed by a turn toward the north-northeast on Monday night. Estimated minimum central pressure is 1011 mb. Maximum sustained wind speed is 35 kt with gusts to 45 kt. Numerous moderate and scattered strong convection is noted within 150 nm eastern semicircle of the low center. The system is expected to remain east of the United States. See latest NHC forecast/ advisory under AWIPS/WMO headers MIATCMAT3/WTNT23 KNHC for more details. ...TROPICAL WAVES... A tropical wave off the west coast of Africa extends from 21N21W to an embedded 1010 mb low near 13N21W to 08N21W, moving W at 15 kt. The low is forecast to move westward over the next couple of days and merge with a broad area of low pressure located southwest of the Cabo Verde Islands. Environmental conditions are expected to become more conducive for development of this system later this week. There is a medium chance for tropical cyclone formation within 5 days. Scattered showers are within 120 nm of the wave axis. A large tropical wave in the eastern Atlantic extends from 22N34W to 08N35W, moving W at 20 kt. The wave shows up very well on the SSMI TPW animation and 700 mb streamline analysis. African dust surrounds the wave to the north and west. Scattered showers are within 90 nm of the wave axis. A tropical wave in the central Atlantic extends from 21N52W to 09N53W. It is moving W at 15-20 kt. The wave coincides with a well defined 700 mb trough, and a high amplitude northward bulge of moisture is noted on the SSMI TPW product. African dust surrounds the wave, which is limiting the associated convective activity. Only scattered showers are seen near the southern end of the wave axis, from 08N-11N between 52W-55W. A tropical wave in the western Caribbean extends from the Yucatan Channel at 22N81W to the NW coast of Costa Rica near 10N86W, moving W at 15 kt. The wave is in a moist area as seen by SSMI TPW imagery. A pronounced 700 mb trough is over the western Caribbean. Scattered moderate convection is over W Cuba. the Yucatan Channel, the Yucatan Peninsula, N Guatemala, W Honduras, and Nicaragua. ...ITCZ/MONSOON TROUGH... The monsoon trough extends from the coast of Africa near 13N17W to 13N27W to 11N35W to 12N42W. The Intertropical Convergence Zone continues from 12N42W to 10N52W to the coast of South America near 09N61W. Aside from the scattered showers associated with the tropical waves, scattered moderate isolated strong convection is noted from 08N-14N between 25W-33W, and from 08N-11N between 37W-42W. ...DISCUSSION... GULF OF MEXICO... A surface trough is analyzed over the NE Gulf from the Florida Panhandle at 30N86W to 27N89W. Scattered showers with embedded thunderstorms are near the trough axis, affecting the NE Gulf waters and N Florida, N of 26N between 80W-90W. The trough will lift northward on Monday, but abundant moisture is expected to persist over the NE Gulf. A ridge is producing a light to gentle anticyclonic flow across the remainder of the Gulf. The ridge will remain across the Gulf waters the next several days. Southerly return flow will freshen over western Gulf by midweek. CARIBBEAN SEA... A tropical wave is moving through the western Caribbean. Please see above. The tropical wave will continue to propagate westward and will be over the Yucatan Peninsula tonight. Scattered moderate convection is over most of Cuba, and NW Haiti. Further S, the eastern extent of the E Pacific monsoon trough is producing scattered moderate convection over, Costa Rica, and Panama. Moderate to fresh winds are over the east and central Caribbean, while mainly light and variable winds are noted over the NW Caribbean. The pressure gradient is forecast to tighten early this week as the Atlantic ridge builds westward in the wake of T.S. Gert. Expect building seas to 8-10 ft with the strongest winds across the south-central Caribbean through midweek. ...HISPANIOLA... Presently, scattered moderate convection is over NW Haiti. Expect daytime heating, local sea breezes and mountain upslope lifting to produce scattered showers and thunderstorms mainly during the afternoon and evening hours Monday. The next tropical wave is forecast to affect the island on Tuesday. ATLANTIC OCEAN... Please see the T.S. Gert, and tropical wave sections above. The remainder of the forecast area is under the influence of the Bermuda-Azores high that is a subtropical high located over the Atlantic Ocean. This high pressure system will build westward across the forecast region as currently T.S.Gert moves northward. Winds are forecast to increase between the eastern tropical wave and strengthening subtropical high to the north. The fresh winds will shift along with the tropical wave as it propagates westward the next couple of days. The Saharan Air Layer tracking product from CIMSS continues to indicate abundant african dust N of 20N E of 30W and between 30W and 50W. For additional information please visit http://www.hurricanes.gov/marine $$ Formosa