000 AXNT20 KNHC 182349 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 748 PM EDT Fri Aug 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 1800 UTC surface analysis and satellite imagery through 2315 UTC. ...SPECIAL FEATURES... Tropical Storm Harvey is located near 13.4N 62.9W at 18/2100 UTC, or about 115 nm WSW of St. Lucia, moving west or 275 degrees at 18 kt. Estimated minimum central pressure is 1005 mb. Maximum sustained wind speed is 35 kt with gusts to 45 kt. The low-level center of Harvey remains near the eastern edge of a strong, but poorly organized, convective area that covers the area from 11N- 15N between 62W-66W. Harvey will move through the eastern Caribbean Sea tonight and through the central Caribbean Sea Saturday and Saturday night. Interests in the Caribbean Sea and the adjacent land areas of eastern Central American and northern South America should monitor the progress of Harvey. Locally heavy rains could occur tonight over portions of the Windward Islands and the offshore islands of northern Venezuela. Locally heavy rains could also occur over Aruba, Bonaire, and Curacao on Saturday. See the latest NHC Intermediate Public Advisory under AWIPS/WMO headers MIATCPAT4/WTNT34 KNHC, and the full Forecast/Advisory under AWIPS/WMO headers MIATCMAT4/WTNT24 KNHC for more details. Shower and thunderstorm activity associated with an area of low pressure located near 18N52W or about 435 nm east-northeast of the Leeward Islands have become less organized since yesterday due to strong upper-level winds, and satellite data suggest that the surface circulation has become less defined. This low pressure area is along a tropical wave than extends from 21N52W to 10N52W. A cluster of strong convection is seen north of the low center and covers the waters from 18N-20N between 51W-53W. Scattered moderate convection is noted elsewhere from 16N-21N between 49W- 54W. Environmental conditions are expected to be only marginally conducive for development during the next couple of days while this system moves west-northwestward at about 20 mph, and the chances for tropical cyclone formation appear to be decreasing. ...TROPICAL WAVES... A tropical wave is in the E Atlantic with axis extending from 20N35W to a 1010 mb low pressure located near 14N36W to 10N36W. Satellite imagery indicates a large cyclonic circulation in the cloud field, but convection is limited in association with this low. Saharan dust surrounds the wave/low. This system coincides with a well defined 700 mb trough, and a high amplitud northward bulge of moisture is noted on the TPW product. Environmental conditions appear somewhat conducive for gradual development over the next few days while the system moves west-northwestward to northwestward at about 18 kt, but upper-level winds are forecast to become unfavorable by the middle of next week. This system has a low change of becoming a tropical cyclone within the next 48 hours. A tropical wave extends from the central Bahamas across eastern Cuba and Jamaica to the SW Caribbean near 10N78W moving W at 15-20 kt. A cluster of moderate to isolated strong convection is along the wave axis between the coast of eastern Cuba and Jamaica. Isolated moderate convection is over the central Bahamas and regional waters. The wave shows up very well on the TPW animation and 700 mb streamline analysis. Moisture associated with this wave will spread across the NW Bahamas and central Cuba by Saturday morning, and across south Florida and western Cuba by Saturday afternoon and evening, increasing the likelihood of showers and thunderstorms, with the potential of locally heavy rain and localized flooding. The tropical wave previously located over the Bay of Campeche is now over Mexico generating some convective activity over the State of Veracruz. For further information about this tropical wave see the Tropical Weather Discussion for the eastern Pacific Ocean. ...ITCZ/MONSOON TROUGH... The monsoon trough extends from the African coast near 13N17W to 12.5N20W to 13N30W to 11N35W to 10N46W. Besides the convection mentioned in the tropical wave and special features sections, scattered moderate convection is from 09N to 12.5N between 20W- 23W. Similar convection is noted within 90 nm S of trough between 37W-41W, and near 12N45W. ...DISCUSSION... GULF OF MEXICO... A weak ridge continues to dominate the Gulf waters. A pair of 1017 mb high centers are noted along the ridge axis, one near the Florida Big Bend and the second one over the NW Gulf. Mainly light to gentle winds are observed under the influence of the ridge. As of 2100 UTC, a surface trough is analyzed from 31N85W to 27N87W. Scatterometer and surface data indicate the wind shift associated with this trough. A thermal trough will develop during the evening hours over the Yucatan Peninsula before pushing offshore into the SW Gulf each night. A surge of fresh winds will accompany this trough. Little change in this weather pattern is expected through early next week. In the upper levels, a large and well- defined upper-level low is spinning over the Florida Keys and western Cuba. This system is helping to induce some shower and thunderstorm activity over the eastern Gulf and the Florida Peninsula. The upper-low will drift westward across the eastern Gulf during the weekend. CARIBBEAN SEA... A tropical wave is over eastern Cuba along 77W/78W. Please, see the Tropical Waves section for details. Tropical Storm Harvey will move through the eastern Caribbean Sea tonight and through the central Caribbean Sea Saturday and Saturday night. Please, see Special Features section for more details. An upper-level low spinning over western Cuba supports scattered showers and tstms. Scattered showers and tstms are also noted over the SW Caribbean, likely associated with the eastern extent of the Pacific monsoon trough combined with a diffluent pattern aloft. ...HISPANIOLA... Daytime heating, local sea breezes and mountain upslope lifting will combined with available moisture to produce isolated to scattered showers and thunderstorms mainly during the afternnon and evening hours. ATLANTIC OCEAN... A pair of tropical waves are moving westward across the tropical Atlantic. The northern portion of a tropical wave is affecting the central Bahamas. Please, see Special Features and Tropical Wave sections above for details. The remainder of the Atlantic is under the influence of a ridge, with a center of 1024 mb located near 32N38W. A belt of fresh to locally strong NE-E winds is noted per scatterometer data roughly between 17N-23N due to the pressure gradient between the ridge and the tropical waves and associated lows located between the coast of Africa and the Lesser Antilles. Fresh to strong Northerly winds are aslo noted between the coast of Africa and the Madeira/Canary Islands. These winds are the result of the pression gradient between the Atlantic ridge and lower pressures over west Africa. For additional information please visit http://www.hurricanes.gov/marine $$ GR