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Tropical Depression NINE Forecast Discussion Number 4

2015-09-17 10:36:51| National Hurricane Center (Atlantic)

Issued at 500 AM AST THU SEP 17 2015 000 WTNT44 KNHC 170836 TCDAT4 TROPICAL DEPRESSION NINE DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092015 500 AM AST THU SEP 17 2015 Tropical Depression Nine continues to have a sheared appearance with an area of strong convection located 75-100 n mi east of the low-level center. Satellite intensity estimates from TAFB and SAB have increased to 30 kt, and reports from NOAA buoy 41041 indicate that the center pressure has fallen below 1007 mb. Based on these data, the initial intensity is increased to 30 kt. The depression is located between a developing upper-level low to its northwest and a tropical disturbance to the southeast. The global models are in poor agreement on how the depression will interact with these systems, which makes for a low confidence intensity forecast. The UKMET and Canadian models merge the depression with the disturbance as the latter system intensifies. The NAVGEM shows the depression surviving for several days as the disturbance weakens. The GFS weakens both the depression and the disturbance while developing another low pressure area nearby. Finally, the ECMWF keeps the depression separate from the other disturbance and forecasts it to survive for five days. Even if the depression and the disturbance do not merge, the upper-level low is likely to cause 20-25 kt of shear over the depression for at least 3-4 days. The new intensity forecast follows the no merger scenario but calls for no additional strengthening due to the shear. The depression is expected to degenerate to a remnant low by 48 hours and dissipate completely after 96 hours. Assuming that the depression and the disturbance do not merge, a weak low- to mid-level ridge to the north of the cyclone should steer it generally northwestward through the forecast period. The new forecast track is similar to the previous track, and it lies to the south of the center of the guidance envelope between the consensus models and the BAM shallow. An alternative forecast scenario is that the depression could move erratically if it and the disturbance get closer enough to try to merge. FORECAST POSITIONS AND MAX WINDS INIT 17/0900Z 16.3N 45.3W 30 KT 35 MPH 12H 17/1800Z 17.1N 45.6W 30 KT 35 MPH 24H 18/0600Z 18.1N 46.3W 30 KT 35 MPH 36H 18/1800Z 19.1N 47.3W 25 KT 30 MPH 48H 19/0600Z 20.0N 48.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 20/0600Z 21.0N 51.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 21/0600Z 22.5N 53.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 22/0600Z...DISSIPATED $$ Forecaster Beven

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Tropical Depression NINE Forecast Discussion Number 3

2015-09-17 04:33:18| National Hurricane Center (Atlantic)

Issued at 1100 PM AST WED SEP 16 2015 000 WTNT44 KNHC 170233 TCDAT4 TROPICAL DEPRESSION NINE DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092015 1100 PM AST WED SEP 16 2015 The depression continues to be sheared with the low-level center well removed from the deep convection. Dvorak T-numbers from all agencies have decreased tonight, but still support an initial intensity of 25 kt. Most of the global models bring even stronger upper-level westerly winds over the cyclone, and this should result in weakening. The depression could still produce intermittent bursts of convection near the center during the next day or so, but the overall trend is for the cyclone to weaken to a remnant low in two days or earlier. The low-level center is difficult to locate on infrared images. The best estimate of the initial motion is toward the northwest or 310 degrees at 6 kt, while embedded within light steering currents. Since the depression is becoming a shallow cyclone, it will likely be steered toward the northwest and then west-northwest by the low-level flow around the subtropical ridge. The NHC forecast is very similar to the previous one, and is on the southern edge of the guidance envelope, leaning toward BAM shallow. FORECAST POSITIONS AND MAX WINDS INIT 17/0300Z 15.8N 45.1W 25 KT 30 MPH 12H 17/1200Z 16.6N 45.4W 25 KT 30 MPH 24H 18/0000Z 17.6N 45.9W 25 KT 30 MPH 36H 18/1200Z 18.8N 46.8W 25 KT 30 MPH 48H 19/0000Z 19.8N 47.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 20/0000Z 21.0N 50.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 21/0000Z 22.0N 52.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 22/0000Z...DISSIPATED $$ Forecaster Avila

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Tropical Depression NINE Forecast Discussion Number 2

2015-09-16 22:33:47| National Hurricane Center (Atlantic)

Issued at 500 PM AST WED SEP 16 2015 000 WTNT44 KNHC 162033 TCDAT4 TROPICAL DEPRESSION NINE DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092015 500 PM AST WED SEP 16 2015 The satellite presentation of the depression has degraded during the past few hours, with dry air and southwesterly shear resulting in the convection become displaced from the low-level center. The convection itself has not become better organized, and has a rather linear shape to the east and northeast of the center. The initial intensity remains 25 kt based on the latest Dvorak estimate from SAB. The prospects for the cyclone to strengthen, or even survive, appear quite poor. The shear is forecast to increase markedly in the next 12 to 24 hours, and the shear in combination with dry air should result in the cyclone weakening to a remnant low by 48 hours. The NHC forecast continues to show dissipation by 5 days, in best agreement with the latest GFS forecast. The exposed low-level center is located about a degree to the west of the previous advisory estimate, with an initial motion of 310/07. The initial position and motion have resulted in a leftward adjustment to the track forecast this cycle of 1 to 2 degrees. The new NHC forecast lies between the shallow BAM and to the left of the rest of the model guidance in the short term given the sheared nature of the system and its current motion. After that time, the NHC forecast is close to the HWRF and GEFS ensemble mean and still left of the multi-model consensus aids. Given the current disorganized state of the depression, the track forecast is quite uncertain through the period. FORECAST POSITIONS AND MAX WINDS INIT 16/2100Z 15.2N 44.6W 25 KT 30 MPH 12H 17/0600Z 15.9N 45.1W 25 KT 30 MPH 24H 17/1800Z 17.0N 45.8W 30 KT 35 MPH 36H 18/0600Z 18.0N 46.4W 25 KT 30 MPH 48H 18/1800Z 19.3N 47.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 19/1800Z 20.5N 49.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 20/1800Z 21.5N 52.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 21/1800Z...DISSIPATED $$ Forecaster Brennan

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Tropical Depression NINE Forecast Discussion Number 1

2015-09-16 16:34:14| National Hurricane Center (Atlantic)

Issued at 1100 AM AST WED SEP 16 2015 000 WTNT44 KNHC 161434 TCDAT4 TROPICAL DEPRESSION NINE DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092015 1100 AM AST WED SEP 16 2015 Organized convection associated with the area of low pressure in the central tropical Atlantic has now increased to the point that the system is considered a tropical cyclone. The initial intensity is 25 kt based on the latest Dvorak classifications and in agreement with earlier ASCAT wind data. Some southwesterly shear is already affecting the cyclone, with most of the convection displaced east and north of the estimated center position. The environment only becomes less favorable from this point forward, with the shear forecast to quickly increase in 12 to 24 hours and remain high through the remainder of the forecast period. In addition, the southwesterly flow aloft will bring dry mid- to upper-level air over the cyclone. As a result, only slight strengthening is shown in the NHC forecast following the trend of most of the intensity guidance. The cyclone is expected to weaken to a remnant low by 72 hours. After that time, the GFS and ECMWF models show the system weakening and perhaps opening up into a trough in about 5 days, so the official forecast shows dissipation at that time. The initial motion estimate is 340/07, as the depression is moving into a weakness in the Atlantic subtropical ridge. This north- northwestward to northwestward motion should continue for the next 2 to 3 days, with a turn toward the west-northwest forecast by 96 hours as the shallow cyclone comes under the steering influence of the low-level trade wind flow. The NHC track forecast is close to the middle of the guidance envelope and near a blend of the GFS and ECMWF forecasts. FORECAST POSITIONS AND MAX WINDS INIT 16/1500Z 15.0N 43.1W 25 KT 30 MPH 12H 17/0000Z 16.0N 43.6W 25 KT 30 MPH 24H 17/1200Z 17.3N 44.1W 30 KT 35 MPH 36H 18/0000Z 18.5N 44.6W 30 KT 35 MPH 48H 18/1200Z 19.7N 45.6W 25 KT 30 MPH 72H 19/1200Z 22.0N 47.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 20/1200Z 24.0N 50.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 21/1200Z...DISSIPATED $$ Forecaster Brennan

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Remnants of HENRI Forecast Discussion Number 12

2015-09-11 22:33:48| National Hurricane Center (Atlantic)

Issued at 500 PM AST FRI SEP 11 2015 000 WTNT43 KNHC 112033 TCDAT3 REMNANTS OF HENRI DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL AL082015 500 PM AST FRI SEP 11 2015 Henri is no longer a tropical cyclone. Visible images clearly show that Henri lacks a well-defined center, with scatterometer and satellite data also suggesting the circulation has degraded into a southeast-to-northwest oriented trough. The scatterometer did show a small area of 35-kt winds, so that intensity is kept. The remnants of Henri are expected to trek northeastward then eastward over the North Atlantic and should transition into an extratropical low on Saturday. Future information on this system can be found in High Seas Forecasts issued by the National Weather Service Ocean Prediction Center...under AWIPS header NFDHSFAT1 and WMO header FZNT01 KWBC. FORECAST POSITIONS AND MAX WINDS INIT 11/2100Z 40.0N 58.5W 35 KT 40 MPH...REMNANTS OF HENRI 12H 12/0600Z...DISSIPATED $$ Forecaster Blake

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