000 AXNT20 KNHC 172350 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 750 PM EDT Thu Aug 17 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... At 17/2100 UTC, Gert becomes a Post-Tropical Cyclone and the last advisory was issued by the National Hurricane Center on this system. At this time, the center of Post-Tropical Cyclone Gert is centered near 44.8N 46.0W or about 745 nm E of Halifax Nova Scotia moving toward the ENE or 60 degrees at 34 kt. Estimated minimum central pressure is 985 mb. Maximum sustained wind speed is 55 kt with gusts to 65 kt. See latest NHC Forecast/Advisory under AWIPS/WMO headers MIATCMAT3/WTNT23 KNHC for more details. At 17/2100 UTC, Potential Tropical Cyclone Nine is upgraded to Tropical Storm Harvey based on reports from an Air Force Reserve Hurricane Hunter Aircraft. At this time, the center of Tropical Storm Harvey is located near 13.0N 55.8W or about 220 nm E of Barbados moving W at 16 kt. Estimated minimum central pressure is 1004 mb. Maximum sustained wind speed has increased to 35 kt with gusts to 45 kt. A cluster of strong convection is noted within about 120 nm west semicircle of center. Scattered moderate to isolated strong convection is elsewhere from 12N-15N between 55W- 59W. Harvey should move through the Windward Islands and into the eastern Caribbean Sea on Friday. Slow strengthening is possible during the next 48 hours. Harvey is expected to produce rainfall totals of 2 to 4 inches across portions of the Windward Islands from Martinique southward to Grenada. These rains could cause life-threatening flash floods and mudslides. See 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. A tropical wave extends from 20N44W to 10N45W. A 1009 mb low pressure is along the wave axis near 15.3N 44.8W. Scattered moderate convection is noted mainly on the west semicircle of the low center from 14N-18N between the wave axis and 47W. The shower and thunderstorm activity associated with this area of low pressure has changed little in organization during the past several hours. However, only a slight increase in the organization of the shower activity could lead to the formation of a tropical depression during the next couple of days before upper-level winds become less favorable for development early next week. The low is expected to move west-northwestward at about 15-20 kt during the next few days, and interests in the northern Leeward Islands should monitor the progress of this disturbance. This system has now a high change of becoming a tropical cyclone through 48 hours. ...TROPICAL WAVES... A tropical wave is moving across the Cabo Verde Islands and extends from 18N24W to 06N25W. A 1010 mb low pressure is along the wave axis near 10N25W. Scattered moderate convection is from 08N-12N between the wave axis and 22W, and ahead of the low center from 06N-10N between 25W-30W. This wave in a very moist area based on TPW imagery and has a well pronounced 700 mb trough. Gradual development of this system is possible through the middle of next week while the wave moves westward to west-northwestward at about 15-20 kt. Currently, this system has a low change of becoming a tropical cyclone through 5 days. A strong and broad tropical wave is moving westward across the Caribbean Sea, and extends along 70W/71W. A cluster of numerous moderate isolated strong convection is noted over the norther part of the wave axis and covers from 18N-21.5N between 68W-71W. This convective activity is affecting the eastern part of Dominican Republic. Scattered moderate isolated strong convection is noted elsewhere from 20N-24N between 66W-72W. The wave shows up very well on the TPW animation and 700 mb streamline analysis. Moisture associated with this wave will spread across the Turks and Caicos Islands, the SE Bahamas, and the remainder of Hispaniola tonight increasing the likelihood of rain. The wave is forecast to move across the SE Bahamas, eastern Cuba and Jamaica on Friday. Fresh to locally strong NE winds are noted over waters ahead of the wave axis. A tropical wave is over the Yucatan Peninsula and Guatemala, with axis along 90W/91W. The wave is helping to induce scattered showers and thunderstorms over parts of the Yucatan peninsula, SE Mexico and Guatemala. The wave coincides with a 700 mb trough, and is well depicted in the moisture product. ...ITCZ/MONSOON TROUGH... The monsoon trough extends from the African coast near 13N16W to a 1010 mb low pressure 10N25W to 09N30W to 10N37W. To the west, the monsoon trough and ITCZ is disrupted due to the tropical systems and tropical waves mentioned above. Otherwise, scattered moderate convection is from 05N-08N between 30W-41W. ...DISCUSSION... GULF OF MEXICO... A 1020 mb high centered over north-central Gulf of Mexico near 27N88W extends a ridge across the region producing mainly gentle to moderate winds based on scatterometer data. 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. The tropical wave currently moving across the Yucatan Peninsula will enhance the presence of this thermal trough tonight. Little change in this weather pattern is expected through early next week. In the upper levels, an upper-level low centered just north of Tampico, Mexico is helping to induce some shower activity over western Gulf, mainly from 20N-23N W of 96W. Isolated showers and tstms are noted over the remainder of the Gulf waters, but particularly from 23N-26N E of 90W. CARIBBEAN SEA... A tropical wave is along 70W/71W, and another tropical wave is over the Yucatan Peninsula. Please, see the Tropical Waves section for details. Tropical Storm Harvey should move through the Windward Islands and into the eastern Caribbean Sea on Friday. Please, see Special Features section for more details. Upper diffluent between an anticyclonic circulation centered over the SE CONUS and an upper-level low spinning over eastern Cuba supports scattered showers and tstms over parts of central and western Cuba. As previously mentioned, a tropical wave now over Hispaniola will bring more showers and tstms over eastern Cuba on Friday, and over western Cuba on Saturday. 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... A strong and broad tropical wave moving across Hispaniola will bring showers and tstms, and gusty winds, with the potential of locally heavy rain tonight and Friday. ATLANTIC OCEAN... A pair of tropical waves and Tropical Storm Harvey are moving westward across the tropical Atlantic. The northern portion of a strong tropical wave is affecting the waters N of Hispaniola. 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 32N41W. A belt of fresh to locally strong NE-E winds is noted per scatterometer data roughly between 15N-22N due to the pressure gradient between the ridge and the tropical systems located between the coast of Africa and the Lesser Antilles. For additional information please visit http://www.hurricanes.gov/marine $$ GR