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Tropical Depression IDA Forecast Discussion Number 32
2015-09-26 10:53:29| National Hurricane Center (Atlantic)
Issued at 500 AM AST SAT SEP 26 2015 000 WTNT45 KNHC 260853 TCDAT5 TROPICAL DEPRESSION IDA DISCUSSION NUMBER 32 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102015 500 AM AST SAT SEP 26 2015 Despite continued westerly shear and abundant dry air in the middle and upper levels of the atmosphere, Ida continues to produce a persistent cluster of deep convection to the east of its center. The intensity remains 30 kt based on ASCAT data from last evening. Ida's future during the next several days is highly uncertain. SHIPS environmental parameters suggest that the worst might be over. The vertical shear that has been affecting the cyclone could actually decrease gradually during the next couple of days, and sea surface temperatures are forecast to remain at least 29 degrees Celsius. Therefore, it is not a sure bet that the system will cease producing organized deep convection, which is a necessary condition for the cyclone to be declared a remnant low. A more likely scenario would be that the circulation becomes elongated, the center becomes ill defined, and Ida dissipates. Therefore, the NHC official forecast no longer shows Ida becoming a remnant low, keeping it as a depression for the next five days. However, Ida could also dissipate at any time if it no longer shows signs of a well-defined center of circulation, as is suggested by the GFS in a couple of days. But, it bears repeating: this is a very uncertain forecast. Ida is being steered northwestward, or 325/7 kt, by a low-level ridge to its northeast. However, the depression is approaching a break in the ridge, and a stronger ridge is expected to slide eastward from New England to the north Atlantic over the next few days. This pattern change should cause Ida to slow down during the next 24 hours and then move westward or west-southwestward at a faster speed during the remainder of the forecast period. The updated NHC track forecast is similar to the previous one, except that it is a little faster beyond 48 hours to be close to the various consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 26/0900Z 23.4N 46.1W 30 KT 35 MPH 12H 26/1800Z 24.0N 46.8W 25 KT 30 MPH 24H 27/0600Z 24.4N 47.6W 25 KT 30 MPH 36H 27/1800Z 24.2N 48.3W 25 KT 30 MPH 48H 28/0600Z 23.6N 49.5W 30 KT 35 MPH 72H 29/0600Z 22.6N 53.3W 30 KT 35 MPH 96H 30/0600Z 22.5N 58.0W 25 KT 30 MPH 120H 01/0600Z 23.0N 61.0W 25 KT 30 MPH $$ Forecaster Berg
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