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Tropical Depression SEVENTEEN-E Forecast Discussion Number 1
2015-09-26 22:33:54| Tropical Depression LIDIA
Issued at 400 PM CDT SAT SEP 26 2015
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Tropical Depression IDA Forecast Discussion Number 34
2015-09-26 22:32:52| National Hurricane Center (Atlantic)
Issued at 500 PM AST SAT SEP 26 2015 000 WTNT45 KNHC 262032 TCDAT5 TROPICAL DEPRESSION IDA DISCUSSION NUMBER 34 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102015 500 PM AST SAT SEP 26 2015 There continues to be little change associated with Ida. A small area of pulsing convection is lingering to the east of the exposed low-level center. The circulation remains well organized, however, and mainly consists of a swirl of low-level clouds. Earlier ASCAT data indicated that winds were in the 25-30 kt range, and since the cyclone has not changed much since then, the initial intensity is held at 30 kt. The models are quite divergent on the future intensity of Ida. The SHIPS model suggests that the depression could strengthen since the shear is expected to lessen during the next 2-3 days. Conversely, most of the dynamical models show little, if any, strengthening likely due in part to the abundant dry air near the cyclone. In fact, the latest runs of the GFS and ECMWF models show Ida's circulation becoming elongated or degenerating into a trough within the next few days when a frontal boundary stalls just to the north of the system. The official forecast follows the previous couple of advisories in maintaining Ida as a depression through the period, however, it would not be surprising if Ida dissipates before then like the GFS and ECMWF models suggest. Ida is gradually turning to the left as predicted, and the latest initial motion estimate is now 320/7 kt. A continued turn toward the west and then southwest is predicted during the next couple of days as a low- to mid-level ridge builds to the north of the cyclone. Thereafter, Ida, or its remnants, is expected to move generally westward at a slightly faster forward speed. Although there remains some spread in the guidance, most of the models agree on this general theme. The new official track forecast is a little faster than the previous one and remains close to the consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 26/2100Z 24.4N 47.1W 30 KT 35 MPH 12H 27/0600Z 24.8N 47.7W 30 KT 35 MPH 24H 27/1800Z 24.6N 48.5W 30 KT 35 MPH 36H 28/0600Z 24.1N 49.6W 30 KT 35 MPH 48H 28/1800Z 23.6N 51.4W 30 KT 35 MPH 72H 29/1800Z 23.4N 55.8W 30 KT 35 MPH 96H 30/1800Z 23.9N 58.9W 25 KT 30 MPH 120H 01/1800Z 24.2N 61.0W 25 KT 30 MPH $$ Forecaster Cangialosi
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Tropical Depression IDA Forecast Discussion Number 33
2015-09-26 16:36:21| National Hurricane Center (Atlantic)
Issued at 1100 AM AST SAT SEP 26 2015 000 WTNT45 KNHC 261436 TCDAT5 TROPICAL DEPRESSION IDA DISCUSSION NUMBER 33 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102015 1100 AM AST SAT SEP 26 2015 There continues to be little change in the satellite appearance of Ida with the low-level center exposed to the west of a persistent area of deep convection. The circulation of the system remains large and well defined. Recent ASCAT data suggest that the initial intensity is still 30 kt, which is a little higher than the Dvorak classifications. The strong westerly shear that has been affecting Ida during the past several days is expected to lessen by tomorrow. Consequently, the SHIPS guidance shows the system gaining strength. However, nearly all of the dynamical models show little, if any, strengthening of Ida. The official forecast continues to prefer the solution provided by the dynamical models due to the continued influence of dry air near the system. It is also possible that the depression could dissipate in a few days when a frontal boundary stalls just to the north of Ida, which could cause the circulation to become elongated or open into a trough. Given the various scenarios provided by the guidance, this forecast is quite uncertain. Ida is still moving north-northwestward at about 7 kt, but it is expected to turn west-northwestward by tonight and southwestward by late tomorrow as a low- to mid-level ridge builds to the north of the system. A general westward motion with some increase in forward speed is expected beyond that time. Although there is some spread in the guidance, most of the models agree on this general theme. A small northward adjustment was made to the previous forecast track beyond 48 hours, to come into better agreement with the latest consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 24.0N 46.5W 30 KT 35 MPH 12H 27/0000Z 24.7N 47.2W 30 KT 35 MPH 24H 27/1200Z 24.9N 47.9W 30 KT 35 MPH 36H 28/0000Z 24.4N 48.7W 30 KT 35 MPH 48H 28/1200Z 23.9N 50.0W 30 KT 35 MPH 72H 29/1200Z 23.5N 53.9W 30 KT 35 MPH 96H 30/1200Z 23.7N 57.7W 25 KT 30 MPH 120H 01/1200Z 24.1N 60.0W 25 KT 30 MPH $$ Forecaster Cangialosi
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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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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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