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Tropical Depression IDA Forecast Discussion Number 28
2015-09-25 10:37:11| National Hurricane Center (Atlantic)
Issued at 500 AM AST FRI SEP 25 2015 000 WTNT45 KNHC 250837 TCDAT5 TROPICAL DEPRESSION IDA DISCUSSION NUMBER 28 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102015 500 AM AST FRI SEP 25 2015 A few convective cells have been forming near Ida's center during the past several hours, but most of the thunderstorm activity remains displaced more than 150 n mi to the east-northeast due to 20 kt of shear. Maximum winds remain 30 kt based on the latest Dvorak CI number from TAFB, but it's clear from satellite imagery that the shear and dry air has caused a steady degradation of the cyclone's structure during the past few days. With moderate vertical shear expected to continue and the mid-level relative humidity forecast to drop to between 30 and 40 percent, additional weakening is anticipated during the next couple of days, and Ida could degenerate to a remnant low by 48 hours. The NHC intensity forecast shows the possibility of the maximum winds increasing again by days 3 and 4, but this is the result of a tight pressure gradient between the remnant low and strong high pressure over the north Atlantic--not a restrengthening of Ida's circulation. Based on global model guidance, the remnant low could open up into a trough by day 5, if not sooner. Ida is being steered generally north-northwestward, or 335/3 kt, by a low-level ridge over the eastern Atlantic. The depression should move northwestward through 48 hours and then abruptly turn westward or west-southwestward during its remnant low stage when strong low-level ridging develops over the north Atlantic. The NHC track forecast is close to the various consensus aids and shows a slightly faster motion of the remnant low after 72 hours compared to the previous forecast. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 21.7N 45.3W 30 KT 35 MPH 12H 25/1800Z 22.4N 45.6W 25 KT 30 MPH 24H 26/0600Z 23.4N 46.4W 25 KT 30 MPH 36H 26/1800Z 24.4N 47.2W 25 KT 30 MPH 48H 27/0600Z 25.0N 47.9W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 28/0600Z 24.1N 49.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 29/0600Z 23.2N 52.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 30/0600Z...DISSIPATED $$ Forecaster Berg
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