| Track: http://www.nhc.noaa.gov/refresh/graphics_at5+shtml/?cone#contents Floater: http://www.ssd.noaa.gov/PS/TROP/floaters/15L/15L_floater.html Wider Atlantic views: http://www.ssd.noaa.gov/PS/TROP/trop-atl.html Potential Tropical Cyclone Fifteen Discussion Number 1 NWS National Hurricane Center Miami FL AL152017 1100 AM AST Sat Sep 16 2017 Satellite images indicate that the area of low pressure located several hundred miles east of the Lesser Antilles has become better organized with curved banding features now better established. Since there is still no indication of a well-defined center and because tropical storm watches have been issued for portions of the Leeward Islands, NHC has initiated advisories on this system as a potential tropical cyclone. The initial wind speed is estimated to be 30 kt based on a blend of the Dvorak classifications from TAFB and SAB. The initial motion estimate is 280/19, but this is uncertain due to the lack of a clear center. A slower west-northwestward motion is expected during the next several days as a mid-level ridge to the north of the system weakens but remains nearly stationary. The NHC track forecast takes the system across the Leeward Islands in a few days and then near the Virgin Islands and Puerto Rico by the end of the forecast period. It should be noted that confidence in the track and forward speed of this system is low due to the spread in the models and the current lack of a well-defined center. The disturbance is expected to be in environmental conditions conducive for strengthening during the next several days as the shear is expected to be 10 kt or less while the cyclone moves over warm 29 deg C SSTs. These conditions should allow for at least steady strengthening, and the models unanimously show that trend. The NHC intensity forecast is conservative for now, but does show the system becoming a tropical storm later today and a hurricane by the time it reaches the Leeward Islands. KEY MESSAGES: 1. The disturbance is expected to intensify and will likely bring tropical storm and hurricane conditions as well as flooding rainfall to portions of the Lesser Antilles early next week. These conditions could also spread into the Virgin Islands and Puerto Rico by mid week. Interests in these areas should monitor the progress of this system and follow any advice given by local officials. FORECAST POSITIONS AND MAX WINDS INIT 16/1500Z 12.2N 50.5W 30 KT 35 MPH...POTENTIAL TROP CYCLONE 12H 17/0000Z 12.8N 52.8W 35 KT 40 MPH...TROPICAL STORM 24H 17/1200Z 13.6N 55.1W 40 KT 45 MPH 36H 18/0000Z 14.3N 56.9W 50 KT 60 MPH 48H 18/1200Z 15.0N 58.6W 60 KT 70 MPH 72H 19/1200Z 16.3N 61.3W 75 KT 85 MPH 96H 20/1200Z 17.6N 64.0W 80 KT 90 MPH 120H 21/1200Z 18.7N 67.3W 80 KT 90 MPH $$ Forecaster Cangialosi Potential Tropical Cyclone Fifteen Advisory Number 1 NWS National Hurricane Center Miami FL AL152017 1100 AM AST Sat Sep 16 2017 ...TROPICAL STORM WATCHES ISSUED FOR A PORTION OF THE LESSER ANTILLES... SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION ----------------------------------------------- LOCATION...12.2N 50.5W ABOUT 755 MI...1220 KM ESE OF THE LESSER ANTILLES MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H PRESENT MOVEMENT...W OR 280 DEGREES AT 22 MPH...35 KM/H MINIMUM CENTRAL PRESSURE...1008 MB...29.77 INCHES WATCHES AND WARNINGS -------------------- CHANGES WITH THIS ADVISORY: The government of St. Lucia has issued a Tropical Storm Watch for St. Lucia. The government of France has issued a Tropical Storm Watch for Martinique and Guadeloupe. The government of Barbados has issued a Tropical Storm Watch for Dominica. SUMMARY OF WATCHES AND WARNINGS IN EFFECT: A Tropical Storm Watch is in effect for... * St. Lucia * Martinique * Guadeloupe * Dominica A Tropical Storm Watch means that tropical storm conditions are possible within the watch area, generally within 48 hours. Interests elsewhere in the Lesser Antilles should monitor the progress of this system. Additional Tropical Storm or Hurricane Watches will likely be issued later today. For storm information specific to your area, please monitor products issued by your national meteorological service. DISCUSSION AND 48-HOUR OUTLOOK ------------------------------ At 1100 AM AST (1500 UTC), the disturbance was centered near latitude 12.2 North, longitude 50.5 West. The system is moving toward the west near 22 mph (35 km/h). A slower west-northwest motion is expected during the next couple of days. On the forecast track, the system is expected to approach the Leeward Islands on Monday. Maximum sustained winds are near 35 mph (55 km/h) with higher gusts. Strengthening is expected during the next 48 hours. The disturbance is forecast to become a tropical storm later today and could be near hurricane strength when it approaches the Leeward Islands. Satellite images indicate that the disturbance has become better organized, and it is expected to become a tropical cyclone later today or tonight. * Formation chance through 48 hours...high...near 100 percent * Formation chance through 5 days...high...near 100 percent The estimated minimum central pressure is 1008 mb (29.77 inches). HAZARDS AFFECTING LAND ---------------------- WIND: Hurricane conditions are possible within portions of Leeward Islands by Monday night or Tuesday, with tropical storm conditions possible on Monday. RAINFALL: The system is expected to produce total rain accumulations of 5 to 10 inches with isolated maximum amounts of 15 inches across portions of the central and southern Leeward Islands through Tuesday night. These rains could cause life-threatening flash floods and mudslides. SURF: Swells generated by the system are expected to begin affecting the Lesser Antilles by Sunday night. These swells are likely to cause life-threatening surf and rip current conditions. Please consult products from your local weather office. NEXT ADVISORY ------------- Next intermediate advisory at 200 PM AST. Next complete advisory at 500 PM AST. $$ Forecaster Cangialosi |