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Tropical Storm Helene Forecast Discussion Number 36

2018-09-16 10:43:14| National Hurricane Center (Atlantic)

Issued at 500 AM AST Sun Sep 16 2018 431 WTNT43 KNHC 160843 TCDAT3 Tropical Storm Helene Discussion Number 36 NWS National Hurricane Center Miami FL AL082018 500 AM AST Sun Sep 16 2018 Helene's cloud pattern is certainly looking less and less like a tropical cyclone this morning. Based on conventional satellite imagery and AMSU data, Helene is quickly undergoing an extratropical transition, and this dynamic process is expected to be completed later today, as the cyclone moves away from the Azores. The initial intensity is lowered to 45 kt, and is based primarily on 2326 UTC ASCAT-A wind retrievals. Cold (22C) sea surface temperatures and strong westerly shear will continue to disrupt Helene's vertical structure and should cause the cyclone to complete the extratropical transition in 12 hours, or sooner. The initial motion is estimated to be northeastward, or 50/22 kt, within the ferocious mid-latitude westerlies. The global models are in remarkably good agreement with Helene accelerating northeastward and becoming absorbed in a large baroclinic zone extending over northern United Kingdom in 72 hours, and the official forecast reflects this scenario. Earlier 2326 UTC METOP-A ASCAT scatterometer data indicated that the 34 kt and 50 kt wind radii, particularly in NW and NE quadrants, had decreased considerably. Accordingly, an adjustment was made on this advisory. Interests in those locations should consult products from their local meteorological service for information about potential impacts from Helene. Local forecasts and warnings for the UK can be found on the website of the UK Met Office athttps://www.metoffice.gov.uk/. Local forecasts and warnings for Ireland can be found on the website of Met Eireann at https://www.met.ie/. FORECAST POSITIONS AND MAX WINDS INIT 16/0900Z 42.5N 28.4W 45 KT 50 MPH 12H 16/1800Z 44.5N 24.7W 45 KT 50 MPH...POST-TROP/EXTRATROP 24H 17/0600Z 47.4N 18.1W 45 KT 50 MPH...POST-TROP/EXTRATROP 36H 17/1800Z 50.8N 10.8W 45 KT 50 MPH...POST-TROP/EXTRATROP 48H 18/0600Z 55.1N 3.7W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 19/0600Z...ABSORBED BY A FRONT $$ Forecaster Roberts

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Tropical Storm Florence Forecast Discussion Number 67

2018-09-16 04:35:06| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Sat Sep 15 2018 350 WTNT41 KNHC 160235 TCDAT1 Tropical Storm Florence Discussion Number 67 NWS National Hurricane Center Miami FL AL062018 1100 PM EDT Sat Sep 15 2018 Florence's center continues to trudge slowly westward across South Carolina, but heavy rainbands are still streaming inland from the ocean across extreme southeastern North Carolina. The NOS station at the Johnny Mercer Pier in Wrightsville Beach in the vicinity of these rainbands is the lone observing station that has still been reporting sustained tropical-storm-force winds, and based on the most recent observations, Florence's maximum winds are estimated to be 35 kt. Florence is expected to weaken to a tropical depression within the next 6-12 hours, with the global model fields showing winds decreasing below 35 kt near the coast very soon. Continued weakening is anticipated while Florence moves farther inland, and it is likely to become a remnant low in about 36 hours when its circulation becomes less defined. Florence is then expected to become a strengthening extratropical low between days 3 and 5 when it exits the Northeast U.S. coast and moves out to sea. The initial motion is still very slow toward the west, or 275/3 kt. A mid-level ridge across the Upper Midwest and Great Lakes is currently blocking Florence from making much headway, but that feature is expected to slide eastward to the western Atlantic during the next 24 hours. This should allow Florence to recurve and accelerate across the Ohio Valley and the northeastern U.S. during the next 3 days, and then accelerate further toward the east-northeast over the Atlantic Ocean on days 4 and 5. The new NHC track forecast is essentially an update of the previous one and is close to the various model consensus aids. Key Messages: 1. Life-threatening, catastrophic flash floods and prolonged significant river flooding are likely over portions of the Carolinas and the southern to central Appalachians from western North Carolina into west-central Virginia and far eastern West Virginia through early next week, as Florence moves slowly inland. In addition to the flash flood and flooding threat, landslides are also possible in the higher terrain of the southern and central Appalachians across western North Carolina into southwest Virginia. 2. Tropical storm conditions will continue along the coast within the tropical storm warning area and also well inland across portions of South Carolina and North Carolina overnight. 3. Large swells affecting Bermuda, portions of the U.S. East Coast, and the northwestern and central Bahamas will continue this week, resulting in life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 16/0300Z 33.7N 80.5W 35 KT 40 MPH...INLAND 12H 16/1200Z 34.3N 81.6W 30 KT 35 MPH...INLAND 24H 17/0000Z 35.8N 83.2W 25 KT 30 MPH...INLAND 36H 17/1200Z 37.8N 83.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 18/0000Z 39.2N 81.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 19/0000Z 41.5N 71.5W 25 KT 30 MPH...POST-TROP/EXTRATROP 96H 20/0000Z 43.0N 59.5W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 21/0000Z 45.5N 47.0W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Berg

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Tropical Storm Joyce Forecast Discussion Number 14

2018-09-16 04:33:40| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Sat Sep 15 2018 705 WTNT45 KNHC 160233 TCDAT5 Tropical Storm Joyce Discussion Number 14 NWS National Hurricane Center Miami FL AL102018 1100 PM AST Sat Sep 15 2018 Joyce is a highly sheared cyclone with the low-level center well separated from the convection. Given the deterioration of the cloud pattern, the initial intensity has been generously set at 35 kt. The shear is expected to remain belligerently high and the ocean along the forecast track is cooler. On this basis, the NHC forecast calls for additional weakening, and then dissipation beyond 3 days if not sooner. Joyce continues to move eastward at about 15 kt embedded within the fast mid-latitude flow. The system should decrease its forward speed as it weakens and become a shallow cyclone. It should then turn east-southeast and even southward steered by the low-level flow. FORECAST POSITIONS AND MAX WINDS INIT 16/0300Z 33.4N 38.0W 35 KT 40 MPH 12H 16/1200Z 34.5N 35.5W 30 KT 35 MPH 24H 17/0000Z 34.5N 32.0W 30 KT 35 MPH 36H 17/1200Z 34.5N 29.0W 30 KT 35 MPH 48H 18/0000Z 33.5N 27.0W 25 KT 30 MPH 72H 19/0000Z 31.0N 27.0W 25 KT 30 MPH 96H 20/0000Z...DISSIPATED $$ Forecaster Avila

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Tropical Storm Helene Forecast Discussion Number 35

2018-09-16 04:32:07| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Sat Sep 15 2018 703 WTNT43 KNHC 160232 TCDAT3 Tropical Storm Helene Discussion Number 35 NWS National Hurricane Center Miami FL AL082018 1100 PM AST Sat Sep 15 2018 The cloud pattern of Helene has continued to be disrupted by the high shear and cold waters. The center is well displaced to the west of the convection, and based on continuity plus the latest Dvorak estimates, the initial intensity is set at 50 kt. Helene is heading toward even colder waters and extremely high shear. This should cause the cyclone to become extratropical in 24 hours or sooner as indicated by the SHIPS guidance. By 72 hours, the cyclone should have been absorbed by a much larger low. Helene is moving toward the northeast or 050 degrees at 22 kt. Since the cyclone is embedded in the westerlies, this general track should continue with an increase in forward speed until dissipation. This is consistent with track models which are in excellent agreement. On the forecast track, Helene should head toward Ireland and the United Kingdom Sunday night and Monday as a strong extratropical cyclone. Interests in those locations should consult products from their local meteorological service for information about potential impacts from Helene. Local forecasts and warnings for the UK can be found on the website of the UK Met Office at https://www.metoffice.gov.uk/. Local forecasts and warnings for Ireland can be found on the website of Met Eireann at https://www.met.ie/. FORECAST POSITIONS AND MAX WINDS INIT 16/0300Z 41.2N 30.1W 50 KT 60 MPH 12H 16/1200Z 43.2N 26.5W 50 KT 60 MPH 24H 17/0000Z 45.5N 21.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 36H 17/1200Z 49.0N 13.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 48H 18/0000Z 53.5N 6.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 19/0000Z...DISSIPATED $$ Forecaster Avila

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Tropical Storm Florence Forecast Discussion Number 66

2018-09-15 22:52:09| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Sat Sep 15 2018 707 WTNT41 KNHC 152052 TCDAT1 Tropical Storm Florence Discussion Number 66 NWS National Hurricane Center Miami FL AL062018 500 PM EDT Sat Sep 15 2018 Florence's center has continued its slow...and I do mean s-l-o-w... westward trek across eastern South Carolina, with little change in the overall structure of the wind field both overland and over water. NOAA WSR-88D Doppler weather radar data, surface observations, and a 1527Z ASCAT pass indicate that Florence is still producing a significant fetch of tropical storm force winds within and adjacent to the the two bands of convection that are currently located between the Cape Fear/Wilmington area and Bogue Inlet, North Carolina. The ASCAT pass contained numerous 40-45 kt wind vectors, and the NOAA NOS observing site at Johnny Mercer Pier in Wrightsville Beach, North Carolina, has been reporting sustained winds of 38-41 kt and gusts to 46-48 kt during the past few hours during the passage of light to moderate rain showers. Therefore, the initial intensity is being maintained at a conservative 40 kt for this advisory. The estimated central pressure of 997 mb is based on nearby surface observations across eastern South Carolina. The initial motion remains 270/02 kt. The new 12Z model guidance remains in excellent agreement on a mid-level ridge currently to the northwest and north of Florence moving steadily eastward during the next 48 hours, which will keep the broad cyclone moving slowly westward to west-northwestward during that time. By 48 hours and beyond, the ridge is forecast to continue to shift eastward to near the northeast U.S. coast and weaken, which will allow Florence and its remnant circulation to move slowly northward into the mid-latitude westerlies by Tuesday. By days 3-5, the global models diverge on where and how fast Florence's then extratropical circulation moves. Due to the significant spread in the guidance, the official forecast track lies close to the consensus model TCVA/TVCN and the previous advisory track forecast. Florence's inner-core convection and wind field will steadily weaken throughout the next 48 hours or so. However, the outer wind field and an associated band of deep convection in the eastern semicircle should continue to produce tropical-storm-force winds for another 12 hours or so over water and near the coast, with occasional strong wind gusts occurring over land. The official intensity forecast is close to an average of the Decay-SHIPS and LGEM, and the IVCN consensus intensity model guidance through 72 hours, and then follows a blend of the IVCN, HCCA, and FSSE consensus models at 96 and 120 hours when the post-tropical cyclone moves back over water and strengthens some due to baroclinic processes. Although coastal storm surge flooding will continue to subside tonight and Sunday, torrential rainfall will continue to be a serious hazard associated with slow-moving Florence. More than two- and-a-half feet of rain has already fallen across portions of southeastern North Carolina, and more rain is still to come, which will cause disastrous flooding that will spread farther inland through the weekend. Key Messages: 1. Life-threatening, catastrophic flash floods and prolonged significant river flooding are likely over portions of the Carolinas and the southern to central Appalachians from western North Carolina into west-central Virginia and far eastern West Virginia through early next week, as Florence moves slowly inland. In addition to the flash flood and flooding threat, landslides are also possible in the higher terrain of the southern and central Appalachians across western North Carolina into southwest Virginia. 2. Water levels along the coast will gradually subside through Sunday. 3. Tropical storm conditions will continue along the coast within the tropical storm warning area and also well inland across portions of South Carolina and North Carolina today. 4. Large swells affecting Bermuda, portions of the U.S. East Coast, and the northwestern and central Bahamas will continue this week, resulting in life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 15/2100Z 33.6N 79.9W 40 KT 45 MPH...INLAND 12H 16/0600Z 33.9N 80.9W 35 KT 40 MPH...INLAND 24H 16/1800Z 35.1N 82.6W 25 KT 30 MPH...INLAND 36H 17/0600Z 37.0N 83.2W 25 KT 30 MPH...INLAND 48H 17/1800Z 38.8N 82.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 18/1800Z 41.4N 74.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 19/1800Z 43.3N 60.8W 30 KT 35 MPH...POST-TROP/EXTRATROP 120H 20/1800Z 47.0N 47.0W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart

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