| TROPICAL STORM IDA DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102015 1100 PM AST FRI SEP 18 2015 The depression's cloud pattern has been increasing in organization. A primarily convective band over the eastern half of the circulation has been increasing in curvature and the cloud tops are cooling significantly. The initial wind speed is increased to 35 kt in agreement with the latest CI numbers from TAFB and SAB and UW-CIMSS ADT value. Westerly shear associated with an upper-level trough, extending from the eastern subtropical Atlantic into the eastern Caribbean, could increase over Ida during the next day or so and slow the cyclone's rate of intensification. Global models agree that a relative reduction in the shear should occur in 2 to 3 days when a piece of the upper-level trough cuts off near the Greater Antilles, which could allow Ida to strengthen, perhaps even more than forecast. Late in the forecast period, the uncertainty in the intensity forecast increases considerably, with the ECMWF calling for more northwesterly shear and less favorable thermodynamic variables in the storm's environment than in the GFS. The new intensity forecast is only slightly higher than the previous one through 72 hours. The forecast after that time is of low confidence and essentially levels Ida's intensity off in agreement with the SHIPS model output. Recent fixes suggest that the cyclone's motion has been more northwesterly (or 305/06) since earlier today. Ida is being steered by east-southeasterly to southeasterly flow underneath a subtropical ridge migrating westward with the cyclone, and some increase in forward speed is predicted by the models during the next day or so. In about 48 hours, a deep-layer trough amplifying southwestward across the eastern Atlantic will cause steering currents surrounding Ida to collapse, which should result in the cyclone's forward motion coming to a halt. With increasing northerly or northwesterly flow aloft, Ida should begin to meander in about 4 days and even drift southward or southeastward by day 5. The new track forecast is adjusted to the right some throughout the period, primarily due to the more northwesterly initial motion but also in the direction of the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 19/0300Z 13.7N 37.5W 35 KT 40 MPH 12H 19/1200Z 14.7N 38.9W 40 KT 45 MPH 24H 20/0000Z 15.8N 40.9W 45 KT 50 MPH 36H 20/1200Z 16.9N 43.2W 50 KT 60 MPH 48H 21/0000Z 18.1N 45.0W 50 KT 60 MPH 72H 22/0000Z 20.1N 47.4W 60 KT 70 MPH 96H 23/0000Z 20.7N 48.0W 55 KT 65 MPH 120H 24/0000Z 20.3N 47.8W 55 KT 65 MPH $$ Forecaster Kimberlain TROPICAL STORM IDA ADVISORY NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102015 1100 PM AST FRI SEP 18 2015 ...TROPICAL STORM IDA FORMS IN THE TROPICAL ATLANTIC... SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION ----------------------------------------------- LOCATION...13.7N 37.5W ABOUT 915 MI...1470 KM W OF THE CAPE VERDE ISLANDS MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H PRESENT MOVEMENT...NW OR 305 DEGREES AT 7 MPH...11 KM/H MINIMUM CENTRAL PRESSURE...1006 MB...29.71 INCHES WATCHES AND WARNINGS -------------------- There are no coastal watches or warnings in effect. DISCUSSION AND 48-HOUR OUTLOOK ------------------------------ At 1100 PM AST (0300 UTC), the center of Tropical Storm Ida was located near latitude 13.7 North, longitude 37.5 West. Ida is moving toward the northwest near 7 mph (11 km/h). A turn toward the west-northwest with an increase in forward speed is expected during the next couple of days. Maximum sustained winds have increased to near 40 mph (65 km/h) with higher gusts. Some slow strengthening is expected during the next 48 hours. Tropical storm force winds extend outward up to 35 miles (55 km) from the center. The estimated minimum central pressure is 1006 mb (29.71 inches). HAZARDS AFFECTING LAND ---------------------- None NEXT ADVISORY ------------- Next complete advisory at 500 AM AST. $$ Forecaster Kimberlain |