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Hurricane Florence Forecast Discussion Number 23

2018-09-05 04:52:38| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Tue Sep 04 2018 797 WTNT41 KNHC 050252 TCDAT1 Hurricane Florence Discussion Number 23 NWS National Hurricane Center Miami FL AL062018 1100 PM AST Tue Sep 04 2018 GOES-16 imagery shows that the eye of Florence has become better defined during the last several hours, with even some mesovortices in the eye present on the shortwave infrared channel. Satellite intensity estimates continue to rise, and the initial wind speed is set to 85 kt, just below the latest TAFB estimate of 90 kt. Florence remains on a west-northwestward course at 300/10 kt. This general course is expected to continue through 36 or 48 hours while the hurricane remains near the southwestern edge of the subtropical ridge. After that time, the forecast becomes more uncertain, depending on the presence of a narrow mid-level ridge over the north-central Atlantic Ocean. A look at the ensemble guidance shows a bifurcation developing by day 5, with the ECMWF favoring a more northward turn, and the UKMET ensembles showing a stronger ridge and a continuation of a west-northwest track. The new NHC forecast is adjusted westward at long range, in line with the corrected-consensus aids, but don't be surprised if this forecast undergoes some large changes in the next few cycles, given the split in the guidance. This intensity forecast is also difficult. Florence certainly has exceeded expectations during the last day or so, with the hurricane on the verge of rapidly intensifying during the last 24 hours despite a marginal environment. Some more strengthening is called for in the short term to reflect the current trend. However, the global models continue to insist that southwesterly shear will increase over the next couple of days which, in combination with considerable dry air aloft, should cause some weakening. Later tomorrow, a slow weakening trend should begin and continue through 48 hours, although not weakening as much as shown in the past advisory. This can't be considered a high-confidence prediction in light of what Florence has done so far. On Friday, an upper-level low could cut off to the south of the cyclone, which would lessen the shear near Florence, and the hurricane should be moving over steadily increasing SSTs. Restrengthening is forecast at long range, and it wouldn't be surprising if the new NHC prediction turns out to be too low. It is best to be conservative, however, since the track uncertainty is increasing by the end of the forecast. FORECAST POSITIONS AND MAX WINDS INIT 05/0300Z 20.7N 43.9W 85 KT 100 MPH 12H 05/1200Z 21.5N 45.5W 90 KT 105 MPH 24H 06/0000Z 22.6N 47.6W 80 KT 90 MPH 36H 06/1200Z 23.7N 49.4W 70 KT 80 MPH 48H 07/0000Z 24.7N 50.9W 65 KT 75 MPH 72H 08/0000Z 26.0N 53.5W 65 KT 75 MPH 96H 09/0000Z 27.3N 55.8W 70 KT 80 MPH 120H 10/0000Z 29.0N 57.5W 80 KT 90 MPH $$ Forecaster Blake

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Hurricane Olivia Forecast Discussion Number 17

2018-09-05 04:47:04| Tropical Depression LIDIA

Issued at 800 PM PDT Tue Sep 04 2018

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Tropical Storm Gordon Forecast Discussion Number 10

2018-09-04 22:52:03| National Hurricane Center (Atlantic)

Issued at 400 PM CDT Tue Sep 04 2018 842 WTNT42 KNHC 042051 TCDAT2 Tropical Storm Gordon Discussion Number 10 NWS National Hurricane Center Miami FL AL072018 400 PM CDT Tue Sep 04 2018 Gordon has been undergoing another convective bursting phase during the past few hours, with a sharp increase in Doppler velocity values noted between 9,000-12,000 ft. Some peak velocity values have been in excess of 80 kt, but average values have been around 65-67 kt, which supports an advisory intensity of 60 kt. Another reconnaissance mission will be conducted in Gordon in a few hours, which provide additional intensity and pressure data. The initial motion estimate is 310/13 kt. There remains no significant change to the previous NHC forecast track or reasoning. The new model guidance has shifted slightly to the east, but not enough to make any appreciable changes to the previous forecast track. As a result, Gordon is expected to move northwestward toward the Mississippi coastline, and the cyclone will make landfall in that area around 0300 UTC. After landfall, steering currents are still expected to weaken, causing Gordon to slow down considerably. The slower forward speed, which will be near 5 kt at times, will act to enhance the heavy rainfall potential. By Friday, a mid- to upper-level trough and a cold front are forecast to cause a break int the subtropical ridge, allowing Gordon to turn northward on Friday, and move northeastward on Saturday. Gordon's remnant circulation is expected to merge with a cold front by Sunday. The new official track forecast is close to a blend of the consensus models HCCA, FSSE, and TVCA, Gordon still has another 6 hours or so over warm waters near 30C, which in combination with an upper-level environment of diffluent southeasterly upper-level flow and increased surface convergence due to land interaction will provide a brief window of opportunity for Gordon to reach hurricane strength before landfall. Once Gordon moves inland, the small circulation is expected to spin down quickly, with Gordon becoming a remnant low by 48 hours. Key Messages: 1. Gordon is expected to bring life-threatening storm surge and hurricane conditions to portions of the central Gulf Coast, where a Storm Surge Warning and Hurricane Warning are in effect. The highest storm surge is expected along the coasts of Mississippi and Alabama from the Mouth of the Pearl River to Dauphin Island tonight and early Wednesday. Tropical storm conditions and storm surge will also affect portions of the western Florida Panhandle. 2. Heavy rainfall from Gordon will affect the western Florida Panhandle, southwest Alabama, southern and central Mississippi, northeastern Louisiana, and southern Arkansas, where totals could reach as high as 12 inches. This rainfall will cause flash flooding in portions of these areas. FORECAST POSITIONS AND MAX WINDS INIT 04/2100Z 29.4N 87.8W 60 KT 70 MPH 12H 05/0600Z 30.7N 89.3W 55 KT 65 MPH...INLAND 24H 05/1800Z 32.2N 90.7W 30 KT 35 MPH...INLAND 36H 06/0600Z 33.2N 91.9W 25 KT 30 MPH...INLAND 48H 06/1800Z 34.0N 93.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 07/1800Z 35.7N 94.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 08/1800Z 38.1N 93.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 09/1800Z 41.0N 89.5W 20 KT 25 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart

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Hurricane Olivia Forecast Discussion Number 16

2018-09-04 22:34:33| Tropical Depression LIDIA

Issued at 200 PM PDT Tue Sep 04 2018

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Hurricane Florence Forecast Discussion Number 22

2018-09-04 22:32:33| National Hurricane Center (Atlantic)

Issued at 500 PM AST Tue Sep 04 2018 669 WTNT41 KNHC 042032 TCDAT1 Hurricane Florence Discussion Number 22 NWS National Hurricane Center Miami FL AL062018 500 PM AST Tue Sep 04 2018 Despite being over marginally warm water and in an environment of moderate west-southwesterly shear, Florence's intensity has increased during the day. The hurricane has a cloud-filled eye in visible imagery, and the central dense overcast is becoming more symmetric. Based on Dvorak estimates of T4.5 from TAFB and SAB, and a SATCON estimate of 77 kt, the initial intensity is now, somewhat surprisingly, 75 kt. Since the current intensification trend may not be over, the official forecast calls for Florence to strengthen just a little more during the next 6-12 hours. Even though the hurricane will be moving over progressively warmer waters, increasing vertical shear and dry air in the middle levels of the atmosphere should induce some weakening in the 24-72 hour time frame. Lower shear after 72 hours will likely allow Florence to regain hurricane strength by the end of the forecast period. The NHC intensity forecast is primarily adjusted to account for the recent strengthening trend, and is closest to the Florida State Superensemble and HCCA guidance. Florence remains on a west-northwestward course at 300/10 kt. This trajectory is expected to continue through 36 hours while the hurricane remains near the southwestern edge of the subtropical ridge. After 36 hours, Florence is expected to turn northwestward and slow down as it enters a break in the ridge. The track models are in good agreement and show little spread through 48 hours. On days 3-5, the biggest outlier is the UKMET, which lies to the south of the guidance suite. In fact, the bulk of the models, including the deterministic GFS and ECMWF, are all now showing a more definitive poleward motion by day 5. While the official NHC track forecast reflects this thinking, there is still considerable spread among the associated global model ensembles, and the longer-term forecast should be considered low confidence. FORECAST POSITIONS AND MAX WINDS INIT 04/2100Z 20.3N 43.2W 75 KT 85 MPH 12H 05/0600Z 21.0N 44.8W 80 KT 90 MPH 24H 05/1800Z 22.1N 46.8W 75 KT 85 MPH 36H 06/0600Z 23.2N 48.7W 65 KT 75 MPH 48H 06/1800Z 24.3N 50.4W 60 KT 70 MPH 72H 07/1800Z 26.0N 53.0W 55 KT 65 MPH 96H 08/1800Z 27.5N 55.0W 60 KT 70 MPH 120H 09/1800Z 29.5N 56.5W 70 KT 80 MPH $$ Forecaster Berg

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