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Post-Tropical Cyclone Juliette Forecast Discussion Number 27

2019-09-07 22:34:56| National Hurricane Center (East Pacific)

Issued at 1100 AM HST Sat Sep 07 2019 000 WTPZ41 KNHC 072034 TCDEP1 Post-Tropical Cyclone Juliette Discussion Number 27 NWS National Hurricane Center Miami FL EP112019 1100 AM HST Sat Sep 07 2019 Juliette has not produced any deep convection for almost 18 hours, and it is therefore being declared a post-tropical cyclone. A recent ASCAT-C pass showed a small area of 30-35 kt winds to the north of the center, and the initial intensity is therefore being set at 35 kt. A gradual spin down of the circulation is expected with Juliette remaining over waters of 24-25C during the next couple of days. After 48 hours, water temperatures do increase a bit to near 26C, but by then incredibly belligerent westerly shear, on the order of 40-50 kt, is expected to be affecting the remnant low. Still, the global models carry a low through the next 5 days, and that is reflected in the official forecast. The initial motion is 280/11 kt. The low should turn on a due west heading for the next 2-3 days, steered by the low-level trade winds. After day 3, the remnant low is expected to interact with a mid- to upper-level low northeast of the Hawaiian Islands, which could cause it to turn northwestward and slow down by day 5. FORECAST POSITIONS AND MAX WINDS INIT 07/2100Z 24.4N 129.5W 35 KT 40 MPH...POST-TROPICAL 12H 08/0600Z 24.4N 131.2W 30 KT 35 MPH...POST-TROP/REMNT LOW 24H 08/1800Z 24.4N 133.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 09/0600Z 24.4N 135.8W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 09/1800Z 24.4N 137.7W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 10/1800Z 24.6N 141.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 11/1800Z 26.0N 144.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 12/1800Z 27.5N 146.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Berg

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Hurricane Dorian Forecast Discussion Number 58

2019-09-07 19:35:55| National Hurricane Center (Atlantic)

Issued at 200 PM AST Sat Sep 07 2019 000 WTNT45 KNHC 071735 TCDAT5 Hurricane Dorian Special Discussion Number 58 NWS National Hurricane Center Miami FL AL052019 200 PM AST Sat Sep 07 2019 This special advisory is being issued instead of the normal intermediate advisory to update the intensity and wind radii of Dorian. A recent ASCAT-B overpass shows a large area of hurricane- force winds southwest and south of the center of Dorian, with many vectors of 80 kt or more. This area of wind is likely due to baroclinic effects during the ongoing extratropical transition. The initial intensity is being increased to 85 kt and the 12-h intensity to 75 kt, after which the forecast intensities are the same as in the previous advisory. Some changes were also made to the initial and 12-h wind radii based on the scatterometer data. There is no change to the forecast track from the previous advisory. Key Messages: 1. Regardless of whether it is a hurricane or a post-tropical cyclone, Dorian is expected to have a significant impact in portions of eastern Canada beginning during the next several hours. Dangerous storm surge impacts are likely in portions of the Gulf of St. Lawrence, southwestern Newfoundland and eastern Nova Scotia. Hurricane-force winds are also likely in Nova Scotia, Prince Edward Island and Newfoundland later today and tonight. Refer to information from the Canadian Hurricane Centre for more information on these hazards. FORECAST POSITIONS AND MAX WINDS INIT 07/1800Z 42.8N 64.9W 85 KT 100 MPH 12H 08/0000Z 45.1N 63.0W 75 KT 85 MPH...INLAND 24H 08/1200Z 48.9N 59.7W 65 KT 75 MPH...POST-TROP/EXTRATROP 36H 09/0000Z 51.7N 54.6W 55 KT 65 MPH...POST-TROP/EXTRATROP 48H 09/1200Z 54.2N 47.8W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 10/1200Z...DISSIPATED $$ Forecaster Beven

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Tropical Storm Gabrielle Forecast Discussion Number 17

2019-09-07 18:14:25| National Hurricane Center (Atlantic)

Issued at 1230 PM AST Sat Sep 07 2019 000 WTNT43 KNHC 071614 TCDAT3 Tropical Storm Gabrielle Special Discussion Number 17 NWS National Hurricane Center Miami FL AL082019 1230 PM AST Sat Sep 07 2019 ASCAT data received just as the previous advisory was issued revealed that Gabrielle's center had re-formed closer to the deep convection, and is about a degree west of where it was previously estimated. This new center is also now more evident in visible satellite imagery. The updated position deviates from the previously issued forecast track by a large enough distance to require the issuance of a special advisory. Based on the re-formation of the center, the longer-term motion is estimated to be west-northwestward, or 300/19 kt. The forecast track has been shifted about a degree westward to account for the corresponding westward relocation of the center. The initial wind radii have been adjusted based on the ASCAT data, which led to an update in the forecast wind radii as well. The initial intensity of 45 kt was confirmed by the scatterometer data, so no changes were made to the intensity forecast. FORECAST POSITIONS AND MAX WINDS INIT 07/1630Z 31.4N 45.2W 45 KT 50 MPH 12H 08/0000Z 32.4N 46.9W 45 KT 50 MPH 24H 08/1200Z 34.0N 48.8W 50 KT 60 MPH 36H 09/0000Z 36.5N 49.0W 55 KT 65 MPH 48H 09/1200Z 39.4N 47.5W 60 KT 70 MPH 72H 10/1200Z 45.0N 38.0W 65 KT 75 MPH 96H 11/1200Z 51.5N 23.5W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 12/1200Z...DISSIPATED $$ Forecaster Berg

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Hurricane Dorian Forecast Discussion Number 57

2019-09-07 16:52:50| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Sat Sep 07 2019 000 WTNT45 KNHC 071452 TCDAT5 Hurricane Dorian Discussion Number 57 NWS National Hurricane Center Miami FL AL052019 1100 AM AST Sat Sep 07 2019 Satellite imagery this morning indicates that Dorian is starting extratropical transition, with cold air clouds entraining into the southwestern side of the cyclone and a developing warm front to the north and east. However, the cyclone still has persistent convection just north and northeast of the center, so it remains a hurricane on this advisory. NOAA buoy 44011 reported a minimum pressure of 955.3 mb as the center passed just to the west, so the initial central pressure is lowered to 953 mb. The initial intensity remains 75 kt based partly on recently-received WindSat data showing hurricane-force winds southwest of the center. Dorian continues to move rapidly northeastward with an initial motion of 040/25 kt. The current motion should bring the center of Dorian over central and eastern Nova Scotia in about 12 h and near or over Prince Edward Island shortly thereafter. Subsequently, Dorian is forecast to move near or through northern Newfoundland and southeastern Labrador before turning east-northeastward over the far north Atlantic. There are no significant changes to the previous forecast, and the new forecast is again close to the various consensus aids. Dorian is expected to complete extratropical transition during the next 24 h as it merges with a strong mid- to upper-level trough and associated surface frontal zone. The global models agree on a gradual decay of the winds after transition is complete. However, the cyclone will likely still be producing hurricane-force winds as it moves through portions of eastern Canada. The global models also agree that the post-tropical cyclone should become absorbed by another extratropical low in 2-3 days. The NHC intensity forecast again leans towards the GFS and ECMWF models, which typically handle large extratropical lows better that than the intensity models that are made for tropical cyclones. Key Messages: 1. Regardless of whether it is a hurricane or a post-tropical cyclone, Dorian is expected to have a significant impact in portions of eastern Canada beginning during the next several hours. Dangerous storm surge impacts are likely in portions of the Gulf of St. Lawrence, southwestern Newfoundland and eastern Nova Scotia. Hurricane-force winds are also likely in Nova Scotia, Prince Edward Island and Newfoundland later today and tonight. Refer to information from the Canadian Hurricane Centre for more information on these hazards. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 42.0N 66.0W 75 KT 85 MPH 12H 08/0000Z 45.1N 63.0W 70 KT 80 MPH...OVER NOVA SCOTIA 24H 08/1200Z 48.9N 59.7W 65 KT 75 MPH...POST-TROP/EXTRATROP 36H 09/0000Z 51.7N 54.6W 55 KT 65 MPH...POST-TROP/EXTRATROP 48H 09/1200Z 54.2N 47.8W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 10/1200Z...DISSIPATED $$ Forecaster Beven

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Tropical Storm Juliette Forecast Discussion Number 26

2019-09-07 16:46:54| National Hurricane Center (East Pacific)

Issued at 500 AM HST Sat Sep 07 2019 000 WTPZ41 KNHC 071446 TCDEP1 Tropical Storm Juliette Discussion Number 26 NWS National Hurricane Center Miami FL EP112019 500 AM HST Sat Sep 07 2019 The last bit of Juliette's deep convection--using -50C cloud tops as a proxy--dissipated around 0400 UTC. Although it's likely that the storm's winds are decreasing, recent satellite estimates range from 25 kt from SAB to 45 kt from TAFB and the UW-CIMSS SATCON. Therefore, the initial intensity will remain 40 kt on this advisory. Although Juliette is now departing a minimum in sea surface temperatures (23-24C), ocean waters ahead of the system will remain below 26C for the next 3 days or so. In addition, west- southwesterly vertical shear will be increasing substantially by 48 hours. If deep convection doesn't redevelop soon, Juliette will become a post-tropical cyclone later today, and then maintain that status with surface winds gradually decreasing over the next several days. The low should open up into a trough around day 5. The initial motion is 280/10 kt. Now that the cyclone has become shallow, it is expected to be steered generally westward by the low-level trade winds. The track models are in good agreement on the future track of Juliette through day 4, and no appreciable changes were required from the previous NHC track forecast. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 24.2N 128.4W 40 KT 45 MPH 12H 08/0000Z 24.3N 130.1W 35 KT 40 MPH...POST-TROPICAL 24H 08/1200Z 24.3N 132.4W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 09/0000Z 24.3N 134.7W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 09/1200Z 24.2N 136.8W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 10/1200Z 24.0N 140.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 11/1200Z 24.5N 143.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 12/1200Z...DISSIPATED $$ Forecaster Berg

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