168 AXNT20 KNHC 260634 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 205 AM EDT Wed Sep 26 2018 Updated Caribbean Sea section 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 0000 UTC surface analysis and satellite imagery through 0545 UTC. ...Special Features... The remnant of Kirk is analyzed as a 1006 mb low near 12N50W or about 565 nm east of the Windward Islands. A tropical wave extends from the low to near 17N, and south of the low to near 04N. This system is moving westward at about 22 kt. The associated shower and thunderstorm activity continues to become better organized. Scattered moderate to strong convection is within 60 nm of the low in the W quadrant. Scattered moderate convection is elsewhere within 90 nm of the low, except 120 nm in the N quadrant. Scattered moderate isolated strong convection is elsewhere within 150 nm east of the low and wave from 09N to 14N and within 90 nm east of the wave from 14N to 17N. Similar convection is elsewhere within 240 nm west of the wave from 08N to 14N, and within 120 nm west of the wave from 14N to 17N. Recent satellite-derived wind data also indicate that the circulation has become better defined and that the winds have increased. If this development trend continues, then advisories will be re-initiated on this system later this morning. Interests in the Windward and Leeward Islands should monitor the progress of this disturbance. An Air Force Reserve reconnaissance aircraft is schedule to investigate this disturbance later today. There is a high chance of redevelopment of this system within the next 48 hours. For more information on this system, see High Seas Forecasts issued by the National Weather Service. Post-Tropical Cyclone Leslie is currently centered about 740 nm west-southwest of the Azores Islands. It is producing gale force winds. Scattered moderate isolated strong convection is seen from 28N to 33N between 37W and 41W. Scattered moderate convection is from 33N to 38N between 38W and 42W. Leslie is expected to reacquire subtropical or tropical characteristics on Thu or Fri while the cyclone meanders over the north-central Atlantic. There is a medium chance of of this system becoming a tropical cyclone during the next 48 hours. For more information on this system, see High Seas Forecasts issued by the National Weather Service. ...TROPICAL WAVES... A far eastern Atlantic tropical wave has its axis along 22W from 03N to 17N, moving westward at 10 to 15 kt. Model guidance depicts a broad 700 mb trough over and near this wave. The satellite- derived low to mid-level nicely display a NE to SE wind shift across the wave. Satellite imagery shows Isolated showers and thunderstorms are within 150 nm west and 120 nm east of the wave axis from 11N to 14N. A tropical wave has is its axis along 50W, with a 1006 mb low on it near 12N60w. This system is described under the Special Features section above. A tropical wave has its axis along 60W south of 19N, moving westward at 15 kt. This wave is shrouded in a very moist and unstable environment as observed in satellite imagery and in the Total Precipitable Water (TPW) satellite animation where it shows a broad pool of moisture. The moisture is noted to be in the form of multilayer clouds, with scattered showers and thunderstorms along the wave, and within 240 nm west of the wave south of 15N. are underneath these clouds from 08N to 15N between 57W and 62W, including the Windward Islands. This activity will continue through at least early this afternoon as a very moist upper southerly flow remains in place across the eastern Caribbean. ...MONSOON TROUGH/ITCZ... The monsoon trough axis extends off the coast of Africa over Senegal at 13N17W and continues to 10N22W to 08N26W, where latest scatterometer data indicated the ITCZ begins and continues to 07N31W to near 07N42W. Outside of the convection mentioned with the two tropical waves and the remnants of Kirk, scattered moderate convection is within 90 nm north of the ITCZ between 28W-34W. Scattered moderate isolated strong convection is within 90 nm north of the ITCZ between 35W-38W and within 60 nm north of the ITCZ between 26W-28W. Scattered moderate convection is within 60 nm south of the ITCZ between 31W-33W. ...DISCUSSION... GULF OF MEXICO... A very moist and unstable air mass along with upper-level diffluence over the north-central Gulf Coast resulted in scattered showers and isolated thunderstorms north of 27N between 84W-90W last night. This activity has since dissipated. Scattered showers and thunderstorms moving westward are over the eastern Gulf from 26N to 29N east of 84W to the Florida coast. This activity fired up yesterday evening along the Florida west coast sea breeze boundary, and has pushed into the eastern Gulf. A thermal trough over the east-central Bay of Campeche is weakening and is no longer producing any significant shower activity. A surface trough will develop over the Yucatan peninsula each evening, shift W over the SW Gulf each night, then dissipate each morning. Elsewhere across the Gulf, gentle to moderate winds will increase to between moderate and fresh during the second half of this week as high pressure builds N of the region. CARIBBEAN SEA...Updated Scattered showers and thunderstorms ahead of a tropical wave that is approaching the Windward Islands have moved into the far eastern Caribbean, and are south of 17N east of 64W to across the Windward Islands. Isolated showers and thunderstorms are elsewhere over the eastern Caribbean. Instability generated by the eastern Pacific monsoon trough that protrudes into the far southwwestern Caribbean, along with low-level speed convergence and to some extent a weak upper low near 12N80W, which is at the base of an upper trough, has recently resulted in a rapid increase of scattered showers and thunderstorms within 60 nm of a line from 09N78W to 12.5N82W to inland the northeast section of Nicaragua from 13N to 15N between 82W and 85W. Scattered moderate convection over the interior sections of Honduras and Nicaragua have just about all diminished. The earlier heaviest part of this activity has shifted to the western sections of these countries. Expect fresh to strong winds over the central Caribbean through midweek, with moderate to fresh winds thereafter through Friday. ATLANTIC OCEAN... Currently, there are three tropical waves in the tropical Atlantic between Africa and the Lesser Antilles. There is also a low with possible tropical cyclone development potential associated with along the wave along 50W. For information on those features, please read the Special Features and Tropical Waves sections above. A surface trough is analyzed from just south of a developing hurricane force wind warning 1000 mb low pressure at 33N43W, south to 26N45W to 24N50W and to 20N60W. Scattered moderate isolated strong convection is within 90 to 120 nm east of the trough north of 25N. A surface trough extends from 28N29W to 22N30W. Only isolated showers are within 60 nm of the trough. Otherwise, ridging over the northeast Atlantic is helping to maintain generally stable and create fair weather north of 20N and east of 30W. For additional information please visit http://www.hurricanes.gov/marine $$ Aguirre