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Tropical Depression NINE Forecast Discussion Number 12

2015-09-19 10:36:02| National Hurricane Center (Atlantic)

Issued at 500 AM AST SAT SEP 19 2015 000 WTNT44 KNHC 190835 TCDAT4 TROPICAL DEPRESSION NINE DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092015 500 AM AST SAT SEP 19 2015 Satellite imagery indicates that Tropical Depression Nine is becoming less organized due to the ongoing 30-35 kt southwesterly shear. The convection is weaker in both coverage and intensity than it was 24 hours ago, and the low-level circulation is losing definition. The shear is expected to continue for at least the next 48 hours, and based on this the depression is expected to degenerate to a remnant low pressure area in 24 hours or less. The initial motion is 290/10. The low- to mid-level subtropical ridge north of the cyclone should steer it or its remnants toward the west-northwest until the system dissipates completely in a couple of days. The new forecast track is an update of the previous track. FORECAST POSITIONS AND MAX WINDS INIT 19/0900Z 18.5N 49.4W 25 KT 30 MPH 12H 19/1800Z 18.9N 50.5W 25 KT 30 MPH 24H 20/0600Z 19.5N 52.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 20/1800Z 20.1N 53.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 21/0600Z 20.9N 55.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 22/0600Z...DISSIPATED $$ Forecaster Beven

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Tropical Storm IDA Forecast Discussion Number 3

2015-09-19 04:54:02| National Hurricane Center (Atlantic)

Issued at 1100 PM AST FRI SEP 18 2015 000 WTNT45 KNHC 190253 TCDAT5 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

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Tropical Depression TEN Forecast Discussion Number 2

2015-09-18 22:34:32| National Hurricane Center (Atlantic)

Issued at 500 PM AST FRI SEP 18 2015 000 WTNT45 KNHC 182034 TCDAT5 TROPICAL DEPRESSION TEN DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102015 500 PM AST FRI SEP 18 2015 The cloud pattern of the depression has continued to improve, with well-defined convective banding wrapping around the center. 1800 UTC Dvorak estimates from TAFB and SAB support tropical storm intensity, but since ASCAT data from earlier this morning only showed 20 kt of wind in the inner core, the initial intensity is only being raised to 30 kt for now. Barring any unexpected changes, the depression will likely be a tropical storm by this evening. The environment appears generally conducive for gradual strengthening during the next few days, but the global models show that the cyclone will be located precariously beneath a narrow upper-level ridge, especially on days 3 through 5. Even a slight deviation from this pattern could put the cyclone in a higher-shear environment and thus limit intensification, or even induce weakening. The NHC intensity forecast continues to show gradual strengthening through the forecast period and is close to a consensus of the SHIPS and LGEM models. The initial motion is 285/7 kt, with the depression being steered by a mid-level anticyclone to its northwest. This anticyclone is expected to move westward at the same pace as the depression during the next few days, maintaining a west-northwestward motion through 48 hours. After that time, the steering currents are forecast to collapse near the cyclone when a deep-layer trough amplifies over the eastern Atlantic. As a result, the models show very slow motion occurring by days 4 and 5, and the updated NHC track forecast shows the cyclone becoming stationary at the end of the forecast period. This forecast is largely unchanged from the previous one and is near the middle of the tightly clustered guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 13.4N 37.3W 30 KT 35 MPH 12H 19/0600Z 13.9N 38.4W 35 KT 40 MPH 24H 19/1800Z 14.9N 40.1W 40 KT 45 MPH 36H 20/0600Z 16.1N 42.5W 45 KT 50 MPH 48H 20/1800Z 17.2N 44.7W 50 KT 60 MPH 72H 21/1800Z 19.5N 47.6W 50 KT 60 MPH 96H 22/1800Z 20.5N 48.5W 55 KT 65 MPH 120H 23/1800Z 20.5N 48.5W 55 KT 65 MPH $$ Forecaster Berg

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Tropical Depression NINE Forecast Discussion Number 10

2015-09-18 22:33:02| National Hurricane Center (Atlantic)

Issued at 500 PM AST FRI SEP 18 2015 000 WTNT44 KNHC 182032 TCDAT4 TROPICAL DEPRESSION NINE DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092015 500 PM AST FRI SEP 18 2015 Deep convection has redeveloped north of the center of the depression this afternoon, buying the system some more time as a tropical cyclone. The initial intensity remains 25 kt based on the latest Dvorak estimates. Given the unfavorable environment of shear and dry air, the system is still expected to become a remnant low in 12 to 24 hours. After that time, the weakening low is expected to open up into a trough as shown by the latest GFS and ECMWF forecasts. The motion of the low-level center has been a little erratic during the past few hours, but a long-term average yields a motion of 300/05. A general west-northwestward motion driven by the low-level ridge to the north is forecast until dissipation, in agreement with the GFS model. The new NHC track is similar to the previous one adjusted for the initial position and motion. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 18.0N 47.3W 25 KT 30 MPH 12H 19/0600Z 18.4N 48.5W 25 KT 30 MPH 24H 19/1800Z 19.0N 50.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 20/0600Z 19.6N 51.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 20/1800Z 20.2N 53.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 21/1800Z...DISSIPATED $$ Forecaster Brennan

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Tropical Depression NINE Forecast Discussion Number 9

2015-09-18 16:33:30| National Hurricane Center (Atlantic)

Issued at 1100 AM AST FRI SEP 18 2015 000 WTNT44 KNHC 181433 TCDAT4 TROPICAL DEPRESSION NINE DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092015 1100 AM AST FRI SEP 18 2015 After the burst of convection overnight, shear and dry air appear to be getting the best of the depression, with no deep convection remaining near the low-level center. If deep convection does not return, the depression could be declared a remnant low by tonight. Weakening is forecast as the depression and its remnant low gradually spin down and dissipate in 3 to 4 days. Visible imagery shows the low-level center has been moving toward the west-northwest with an initial motion estimate of 295/7. The initial position and motion have resulted in a leftward shift of the NHC track forecast this cycle of about a degree. The NHC forecast shows the shallow cyclone moving generally west-northwestward through dissipation as it is steered by the low-level ridge to the north. The official forecast continues to favor the weaker models, such as the GFS and the GEFS ensemble mean, on the left side of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 18/1500Z 17.7N 47.1W 25 KT 30 MPH 12H 19/0000Z 18.2N 48.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 19/1200Z 18.9N 49.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 20/0000Z 19.6N 51.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 20/1200Z 20.4N 52.9W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 21/1200Z 21.5N 55.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 22/1200Z...DISSIPATED $$ Forecaster Brennan

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