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Tropical Storm VANCE Forecast Discussion Number 24

2014-11-05 03:47:15| National Hurricane Center (East Pacific)

Issued at 700 PM PST TUE NOV 04 2014 000 WTPZ41 KNHC 050247 TCDEP1 TROPICAL STORM VANCE DISCUSSION NUMBER 24 NWS NATIONAL HURRICANE CENTER MIAMI FL EP212014 700 PM PST TUE NOV 04 2014 The convective organization of Vance has continued to erode significantly since the previous advisory due to strong south-southwesterly vertical wind shear in excess of 45 kt and entrainment of drier air. As a result, the initial intensity has been decreased to 45 kt based on a blend of various satellite intensity estimates. Additional rapid weakening is expected until landfall occurs in about 18 hours or so, and Vance could be a tropical depression at that time. After landfall, Vance is expected to quickly dissipate over the mountainous terrain of northwestern Mexico. The initial motion estimate is 025/12 kt. There is no significant change to the previous forecast track or reasoning. Vance is expected to remain embedded within south-southwesterly flow on the east side of deep-layer trough for the next 24 hours, which should result in a north-northeastward motion until landfall occurs. Moisture from Vance is spreading northeastward across Mexico and into the south-central United States. This is producing heavy rains over portions of these areas which should continue through Thursday or Friday. FORECAST POSITIONS AND MAX WINDS INIT 05/0300Z 21.5N 108.0W 45 KT 50 MPH 12H 05/1200Z 23.1N 107.2W 30 KT 35 MPH 24H 06/0000Z 25.3N 106.4W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 06/1200Z...DISSIPATED $$ Forecaster Stewart

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Tropical Storm VANCE Forecast Discussion Number 23

2014-11-04 21:41:14| National Hurricane Center (East Pacific)

Issued at 100 PM PST TUE NOV 04 2014 000 WTPZ41 KNHC 042041 TCDEP1 TROPICAL STORM VANCE DISCUSSION NUMBER 23 NWS NATIONAL HURRICANE CENTER MIAMI FL EP212014 100 PM PST TUE NOV 04 2014 The organization of Vance has decreased significantly over the past several hours due to the effects of 50-60 kt of vertical wind shear. The low-level center is now exposed to the southwest of the main convective mass, and the convection has decreased in both coverage and intensity. The initial intensity is lowered to 55 kt, and this again could be a little generous. The initial motion is 030/12. The guidance has trended eastward and faster since the last advisory, and the dynamical models now forecast the cyclone to make landfall over mainland Mexico in 18-24 hours. The new forecast track lies a little to the east of the previous track, but is west of, and slower than, the consensus models. Continuing strong shear should cause additional rapid weakening. The majority of the guidance forecasts Vance to weaken below tropical-storm strength before landfall, and the new intensity forecast follows that scenario. However, given the uncertainties in intensity prediction it remains prudent to have a tropical storm watch for portions of the coast of Mexico. After landfall, Vance is expected to dissipate over the mountains of northwestern Mexico. Moisture from Vance and its remnants is spreading northeastward across Mexico and into the south-central United States. This is producing heavy rains over portions of these areas which should continue through Thursday or Friday. FORECAST POSITIONS AND MAX WINDS INIT 04/2100Z 20.4N 108.6W 55 KT 65 MPH 12H 05/0600Z 22.1N 107.8W 40 KT 45 MPH 24H 05/1800Z 24.4N 106.9W 25 KT 30 MPH...INLAND 36H 06/0600Z 26.5N 106.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 06/1800Z...DISSIPATED $$ Forecaster Beven

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Hurricane VANCE Forecast Discussion Number 22

2014-11-04 15:39:42| National Hurricane Center (East Pacific)

Issued at 700 AM PST TUE NOV 04 2014 000 WTPZ41 KNHC 041439 TCDEP1 HURRICANE VANCE DISCUSSION NUMBER 22 NWS NATIONAL HURRICANE CENTER MIAMI FL EP212014 700 AM PST TUE NOV 04 2014 Conventional and microwave satellite data indicate that Vance is losing organization due to the effects of 35-40 kt of vertical wind shear. The cloud pattern has become elongated, and the low-level center is near the southern edge of the convection. The initial intensity is lowered to 75 kt based on various satellite intensity estimates, and this could be a bit generous. The initial motion is 025/11. The GFS, ECMWF, GFDL, and Florida State Superensemble models forecast Vance to move generally northeastward and make landfall on the coast of Mexico in 24-36 hours. The official forecast does likewise, and the new forecast is similar to that of the previous advisory. It cannot be ruled out that Vance will completely shear apart before landfall, with the low-level center moving slower toward the northeast than currently forecast. The large-scale models forecast even stronger shear over Vance during the next 24-36 hours, and this should cause rapid weakening. The new intensity forecast follows this scenario and is in best agreement with the SHIPS model. Although Vance could weaken to a depression by the time it makes landfall, given the uncertainties in intensity prediction it remains prudent to have a tropical storm watch for portions of the coast of Mexico. Moisture from Vance and its remnants should spread northeastward across Mexico and into the south-central United States during the next several days. This is likely to produce heavy rains over portions of these areas through Thursday or Friday. FORECAST POSITIONS AND MAX WINDS INIT 04/1500Z 19.3N 109.6W 75 KT 85 MPH 12H 05/0000Z 21.0N 108.7W 60 KT 70 MPH 24H 05/1200Z 23.2N 107.8W 40 KT 45 MPH 36H 06/0000Z 25.3N 107.2W 25 KT 30 MPH...INLAND 48H 06/1200Z...DISSIPATED $$ Forecaster Beven

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Hurricane VANCE Forecast Discussion Number 21

2014-11-04 09:38:11| National Hurricane Center (East Pacific)

Issued at 100 AM PST TUE NOV 04 2014 000 WTPZ41 KNHC 040838 TCDEP1 HURRICANE VANCE DISCUSSION NUMBER 21 NWS NATIONAL HURRICANE CENTER MIAMI FL EP212014 100 AM PST TUE NOV 04 2014 Satellite images indicate that the anticipated weakening of Vance has begun. The cloud pattern has become decidedly less circular and more ragged over the past several hours, and the overall coverage of deep convection is gradually decreasing. The current intensity is set at 90 kt in agreement with a Dvorak estimate from TAFB, although this may be generous given the most recent satellite presentation. More than 30 kt of south-southwesterly vertical shear is currently affecting the hurricane, and this shear is forecast to increase to about 45-55 kt in 24 to 36 hours. Vertical cross sections from the latest GFS model forecast show that most of the tropical cyclone's circulation above 500 mb is removed within the next 24 hours, presumably due to the intense shear. These very hostile dynamical conditions should result in a rather rapid rate of weakening before the tropical cyclone nears the Mexican coast. The official intensity forecast closely follows the latest SHIPS prediction. Although Vance could weaken to a depression by the time it reaches the coast, given the uncertainties in intensity prediction, it is prudent to have a tropical storm watch at this time. It is estimated that the low-level center is near the southwestern edge of the main convective mass, and the initial motion estimate of 025/11 kt is not much different from the previous package. Vance is expected to continue moving north-northeastward to the south and southeast of a mid-level trough over the next day or two. The official track forecast lies between the latest GFS and ECMWF predictions, and lies a little to the east of the multi-model consensus. Moisture from Vance and its remnants should spread northeastward across Mexico and into the south-central United States during the next several days. This is likely to produce heavy rains over portions of these areas through Thursday or Friday. FORECAST POSITIONS AND MAX WINDS INIT 04/0900Z 18.4N 110.0W 90 KT 105 MPH 12H 04/1800Z 19.8N 109.3W 70 KT 80 MPH 24H 05/0600Z 22.0N 108.4W 50 KT 60 MPH 36H 05/1800Z 24.1N 107.6W 30 KT 35 MPH 48H 06/0600Z 26.0N 107.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 07/0600Z...DISSIPATED $$ Forecaster Pasch

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Hurricane VANCE Forecast Discussion Number 20

2014-11-04 03:54:39| National Hurricane Center (East Pacific)

Issued at 700 PM PST MON NOV 03 2014 000 WTPZ41 KNHC 040254 TCDEP1 HURRICANE VANCE DISCUSSION NUMBER 20...CORRECTED NWS NATIONAL HURRICANE CENTER MIAMI FL EP212014 700 PM PST MON NOV 03 2014 Corrected text to read tropical storm watch issued Vance has maintained a well-defined central dense overcast pattern since the previous advisory, although the eye has become less distinct in infrared and recent SSMI/S microwave imagery. However, cloud tops colder than -80C now completely encircle the remnant eye feature in infrared imagery. An average of Dvorak current intensity estimates yields a value of 96 kt, so the initial intensity is being maintained at 95 kt. Vance has started to recurve to the north-northeast and the initial motion estimate is now 020/11 kt. The hurricane is expected to move in a general north-northeastward to northeastward direction within south-southwesterly steering flow between the subtropical ridge to the east and an approaching deep-layer trough to the west. As a result, Vance is expected to pass just east of Socorro Island tonight and be near the southwestern coast of Mexico in 48 hours or so. The NHC model guidance is in decent agreement on this scenario, and the official forecast track is just an update of the previous advisory track and lies close to the blend of the GFS and ECMWF model solutions. The latest SHIPS guidance indicates south-southwesterly vertical wind shear of at least 30 affecting Vance. Although this estimate could be a little overdone given the impressive infrared satellite signature, a 0134 UTC SSMI/S microwave overpass suggests that the circulation is starting to tilt downstream to the northeast due to the shear. The vertical shear is forecast by all of the global models to steadily increase throughout the forecast period, which should result in steady or rapid weakening until landfall occurs in about 48 hours. The official intensity forecast is similar to the previous advisory and is close to a blend of the SHIPS and LGEM models, which is just slightly above the consensus model ICON. The forecast still calls for Vance to become a tropical depression just offshore of the coast of southwestern Mexico. However, due to the uncertainty in the exact timing of the expected weakening trend, the Government of Mexico has issued a tropical storm watch for portions of southwestern mainland Mexico. Moisture from Vance and its remnants should spread northeastward across Mexico and into the south-central United States during the next several days. This is likely to produce heavy rains over portions of these areas through Thursday or Friday. FORECAST POSITIONS AND MAX WINDS INIT 04/0300Z 17.4N 110.6W 95 KT 110 MPH 12H 04/1200Z 18.8N 110.1W 75 KT 85 MPH 24H 05/0000Z 20.5N 109.1W 60 KT 70 MPH 36H 05/1200Z 22.7N 108.3W 45 KT 50 MPH 48H 06/0000Z 24.6N 107.9W 30 KT 35 MPH 72H 07/0000Z 25.5N 108.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 08/0000Z...DISSIPATED $$ Forecaster Stewart

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