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Tropical Depression IDA Forecast Discussion Number 31
2015-09-26 04:51:18| National Hurricane Center (Atlantic)
Issued at 1100 PM AST FRI SEP 25 2015 000 WTNT45 KNHC 260251 TCDAT5 TROPICAL DEPRESSION IDA DISCUSSION NUMBER 31 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102015 1100 PM AST FRI SEP 25 2015 The depression consists of a swirl of low clouds with pulsing convection in the eastern part of the circulation. Although Ida isn't very impressive on satellite imagery, the latest ASCAT data showed a small area of 30-35 kt winds in the southeastern quadrant of the cyclone. Since the convective structure has degraded since the ASCAT pass and the Dvorak estimates are low, the initial wind speed is conservatively set to 30 kt. Ida is still forecast, albeit with low confidence, to decay into a remnant low in 24 h while the cyclone remains in a high shear, low moisture environment during the next day or so. Global and regional model guidance, however, are starting to suggest that Ida will encounter a more favorable environment in 2-3 days with less shear and warmer waters, with only the GFS model now showing dissipation. In fact, most of the guidance brings the cyclone back to tropical storm strength by day 5. I'd like to see more consistent guidance before forecasting that solution, but as a compromise, the new prediction calls for Ida to regenerate as tropical depression, but with limited strengthening. While the new forecast is above the previous one, it is below almost all of the guidance except for the GFS. Ida is moving faster toward the north-northwest tonight at about 7 kt. The cyclone is forecast to turn northwestward tomorrow, westward on Sunday and then west-southwestward while Ida moves around a strengthening mid-level ridge over the central Atlantic. Models have come into better agreement on this scenario, although the ECMWF remains a bit of a slow outlier. The official forecast is shifted southwestward, but lies on the northern side of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 22.9N 45.5W 30 KT 35 MPH 12H 26/1200Z 23.6N 46.3W 30 KT 35 MPH 24H 27/0000Z 24.3N 47.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 27/1200Z 24.3N 47.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 28/0000Z 23.7N 48.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 29/0000Z 22.7N 51.5W 30 KT 35 MPH 96H 30/0000Z 22.1N 54.6W 30 KT 35 MPH 120H 01/0000Z 22.5N 57.5W 30 KT 35 MPH $$ Forecaster Blake
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