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Tropical Storm Lee Forecast Discussion Number 48

2017-09-30 04:33:05| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Fri Sep 29 2017 000 WTNT44 KNHC 300232 TCDAT4 Tropical Storm Lee Discussion Number 48 NWS National Hurricane Center Miami FL AL142017 1100 PM AST Fri Sep 29 2017 Lee has been devoid of deep convection for the past 6 hours due to strong northwesterly vertical wind shear and sea-surface temperatures near 20 deg C. The initial intensity has been lowered to 50 kt based on a UW-CIMSS ADT intensity estimate of 51 kt and typical decay rate for tropical cyclones at that latitude. Lee is forecast to become an extratropical low in the next 6-12 h due to aforementioned strong shear and cold ocean temperatures. However, due to a continued increase in forward speed, little change in strength is expected until dissipation occurs in 12-24 hours despite the lack of any significant convection with the system. Lee has continued to accelerate toward the northeast, and the initial motion estimate is now 060/36 kt. For the next day or so, Lee will remain embedded within deep-layer southwesterly flow ahead of a mid-/upper-level trough, and continue to accelerate toward the northeast. Since the models remain tightly clustered, no change was made to the previous forecast track. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 44.3N 42.8W 50 KT 60 MPH 12H 30/1200Z 47.8N 33.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 24H 01/0000Z...DISSIPATED $$ Forecaster Stewart

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Tropical Storm Maria Forecast Discussion Number 55

2017-09-29 22:36:33| National Hurricane Center (Atlantic)

Issued at 500 PM AST Fri Sep 29 2017 000 WTNT45 KNHC 292036 TCDAT5 Tropical Storm Maria Discussion Number 55 NWS National Hurricane Center Miami FL AL152017 500 PM AST Fri Sep 29 2017 The cloud pattern has deteriorated and the only convection left is is a curved band of thunderstorms to the east of the center. Latest SSMI microwave data clearly indicate that the low- and mid- level centers are rapidly becoming separated. However, Dvorak estimates still call for an initial intensity of 50 kt at this time. Cold air continues to entrain into the cyclone and Maria has probably already began to acquire extratropical characteristics. Given the cold water along the forecast track, Maria will probably become extratropical in about 36 hours or even sooner. The track is straightforward since the cyclone is well embedded in the mid-latitude westerlies. This flow pattern will continue to steer Maria on a general east-northeast track with increasing forward speed until dissipation over the cold waters of the North Atlantic. The NHC forecast incorporates guidance provided by the NOAA Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 29/2100Z 37.8N 57.4W 50 KT 60 MPH 12H 30/0600Z 39.0N 52.5W 50 KT 60 MPH 24H 30/1800Z 41.5N 45.5W 50 KT 60 MPH 36H 01/0600Z 44.0N 38.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 01/1800Z 47.5N 30.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 02/1800Z...ABSORBED $$ Forecaster Avila

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Tropical Storm Lee Forecast Discussion Number 46

2017-09-29 16:48:28| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Fri Sep 29 2017 000 WTNT44 KNHC 291448 TCDAT4 Tropical Storm Lee Discussion Number 46 NWS National Hurricane Center Miami FL AL142017 1100 AM AST Fri Sep 29 2017 Lee continues to accelerate toward the northeast, and the estimated motion is now 045/27 kt. Due to continued strong northerly shear, the low-level center of Lee is exposed and deep convection is confined to the southeast quadrant of the cyclone. No new ASCAT data has been available since yesterday evening, but some weakening since the last advisory is assumed, given the limited extent of convection. The initial intensity has been lowered to 60 kt, making Lee a tropical storm. Lee is crossing a tight SST gradient north of the Gulf Stream, and will be passing over SSTs below 23 deg C within the next couple of hours. The cold SSTs, plus continued high shear, should cause the circulation of Lee to continue to spin down over the next day or two, while the cyclone continues to accelerate toward the northeast. Some of Lee's spin-down will likely be offset by the increasing forward speed of the cyclone, limiting how much the wind speed can decrease, but the dynamical models still forecast that Lee will open up into a trough in 24 to 36 h. Very little change has been made to the NHC track or intensity forecasts, which remain close to the track and intensity consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 40.1N 49.5W 60 KT 70 MPH 12H 30/0000Z 43.1N 43.9W 55 KT 65 MPH 24H 30/1200Z 47.6N 32.8W 55 KT 65 MPH 36H 01/0000Z...DISSIPATED $$ Forecaster Zelinsky

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Tropical Storm Maria Forecast Discussion Number 54

2017-09-29 16:40:04| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Fri Sep 29 2017 000 WTNT45 KNHC 291439 TCDAT5 Tropical Storm Maria Discussion Number 54 NWS National Hurricane Center Miami FL AL152017 1100 AM AST Fri Sep 29 2017 Although Maria is trying to race east-northeastward ahead of a cold front, satellite images indicate that cold air is already beginning to entrain into the circulation of the tropical cyclone. Most of deep convection is limited to a curved band to the east of the center and an average of Dvorak estimates indicate that the maximum winds are still 50 kt. The winds could increase a little due to baroclinic forcing later today while Maria acquires extratropical characteristics. Maria should become post-tropical in about 36 hours, and then dissipate or be absorbed by a larger cyclone around day 3. Maria is already embedded in the mid-latitude westerlies and is racing toward the east-northeast at 27 kt. This steering pattern is forecast to persist, and Maria is anticipated to continue on this track with an increase in forward speed until dissipation. The NHC forecast uses guidance provided by the NOAA Ocean Prediction Center and is also in very good agreement with track models. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 37.5N 60.1W 50 KT 60 MPH 12H 30/0000Z 38.6N 55.3W 55 KT 65 MPH 24H 30/1200Z 40.5N 48.5W 55 KT 65 MPH 36H 01/0000Z 43.5N 40.5W 55 KT 65 MPH...POST-TROP/EXTRATROP 48H 01/1200Z 46.5N 32.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 02/1200Z...DISSIPATED $$ Forecaster Avila

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Hurricane Lee Forecast Discussion Number 45

2017-09-29 10:51:32| National Hurricane Center (Atlantic)

Issued at 500 AM AST Fri Sep 29 2017 000 WTNT44 KNHC 290851 TCDAT4 Hurricane Lee Discussion Number 45 NWS National Hurricane Center Miami FL AL142017 500 AM AST Fri Sep 29 2017 Lee's low-level center is partially exposed along the northern edge of the convective canopy due to almost 40 kt of northerly shear. ASCAT data from last evening showed winds as high as 70 kt, so assuming some weakening due to the belligerent shear, the initial intensity is lowered to 65 kt. Lee will be crossing the tight SST gradient to the north of the Gulf Stream within the next 6-12 hours, and along with continued strong shear, this should cause the cyclone to weaken further and become a tropical storm later today. Global model guidance then indicates that Lee will dissipate in the fast flow ahead of an approaching cold front by 36 hours. Even after Lee's circulation opens up, a swath of strong winds will likely continue eastward toward Ireland and the United Kingdom by days 2 and 3. Lee is accelerating northeastward with an initial motion of 040/22 kt. The cyclone should maintain that heading with its speed increasing further up until the time it dissipates. The track guidance is tightly clustered for the next 24 hours before dissipation, and the NHC forecast is mainly an update of the previous one. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 38.3N 52.4W 65 KT 75 MPH 12H 29/1800Z 41.1N 48.0W 60 KT 70 MPH 24H 30/0600Z 45.4N 39.3W 50 KT 60 MPH 36H 30/1800Z...DISSIPATED $$ Forecaster Berg

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