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Hurricane Olivia Forecast Discussion Number 31
2018-09-08 10:52:34| Tropical Depression LIDIA
Issued at 200 AM PDT Sat Sep 08 2018
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Tropical Storm Helene Forecast Discussion Number 4
2018-09-08 10:51:02| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sat Sep 08 2018 380 WTNT43 KNHC 080850 TCDAT3 Tropical Storm Helene Discussion Number 4 NWS National Hurricane Center Miami FL AL082018 500 AM AST Sat Sep 08 2018 Helene's structure appears to be quickly improving this morning. The initial intensity has been increased to 40 kt based on a blend of the latest subjective Dvorak intensity estimates and the UW-CIMSS SATCON. Several microwave passes overnight indicate that the cyclone has become more vertically aligned, likely due to a reformation of the center beneath the strongest convection. In fact, a 0733 UTC SSMIS image shows the early development of a low- to mid-level eye, which is often a precursor to intensification. Nearly all of the intensity guidance seems to have picked up on the improved structure of Helene, and the models show far more intensification than before, especially through 48 h. Consequently, a significant change has been made to the intensity forecast, which now calls for Helene to become a hurricane on Sunday while it is near the Cabo Verde islands. Once the cyclone passes the islands, the environment is expected to remain favorable for intensification for at least 72 h. By the end of the forecast period, all of the guidance shows some weakening due primarily to increased shear associated with an approaching mid- to upper-level trough over the central Atlantic. Given the recent microwave imagery signature, low shear, and warm SSTs, its possible that the current forecast is still too conservative, especially for the first 36 h of the forecast, and further adjustments could be required if it becomes clear that Helene is intensifying at a faster rate than expected. Smoothing through the possible reformation of the center, Helene appears to be moving west with an initial motion around 275/10 kt. Little change was required to the track forecast, which has been nudged only slightly south for the first 48 h of the forecast, in line with the latest track model consensus. A westward motion should continue for the next couple of days, as Helene is steered by a mid-level ridge to the north. By day 5, the aforementioned trough over the central Atlantic should force Helene to turn toward the northwest. FORECAST POSITIONS AND MAX WINDS INIT 08/0900Z 13.7N 19.6W 40 KT 45 MPH 12H 08/1800Z 13.9N 21.2W 50 KT 60 MPH 24H 09/0600Z 14.1N 23.5W 60 KT 70 MPH 36H 09/1800Z 14.7N 26.3W 70 KT 80 MPH 48H 10/0600Z 15.4N 29.3W 75 KT 85 MPH 72H 11/0600Z 17.2N 35.1W 80 KT 90 MPH 96H 12/0600Z 19.0N 39.5W 70 KT 80 MPH 120H 13/0600Z 22.0N 42.5W 65 KT 75 MPH $$ Forecaster Zelinsky
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Tropical Storm Florence Forecast Discussion Number 36
2018-09-08 10:46:04| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sat Sep 08 2018 151 WTNT41 KNHC 080845 TCDAT1 Tropical Storm Florence Discussion Number 36 NWS National Hurricane Center Miami FL AL062018 500 AM AST Sat Sep 08 2018 Although Florence remains a sheared tropical cyclone, satellite imagery during the past 6 h also indicates that the shear has started to abate somewhat, which has allowed the dense cirrus canopy to build back over the previously exposed low-level circulation center. Furthermore, deep convection with overshooting cloud tops near -80C and an abundance of lightning activity have developed very close to the center. Based on these data along with Dvorak intensity estimates of T3.5/55 kt from TAFB and SAB, the initial intensity has been raised to 55 kt. The initial motion estimate is 265/8 kt. The mid-latitude flow across CONUS and the northern Atlantic is forecast to flatten out and become more zonal over the next 48 h or so, resulting in the development of a narrow east-west oriented ridge along 35/36N latitude. This large-scale feature is expected to steer Florence in a general westward direction during that time. By days 3-5, however, the flow across the central and western U.S. is forecast to buckle and become more meridional as a deep mid-/upper-level trough over the northeast Pacific pushes inland over the western U.S., causing downstream ridging over the northeastern U.S. and northwestern Atlantic. The global models agree on this general change in the synoptic-scale flow pattern, but they differ noticeably on where a downstream mid-/upper-level high pressure cell takes up residence over the Atlantic either to the northwest or northeast of Bermuda. The farther west/east the high develops will determine how far west/east Florence will eventually move and possibly affect the U.S. east coast beyond the 5-day forecast period. The new official forecast track is close to the previous advisory track through 48 h, and then was nudged a little to the left or west of the previous track, which is close to the consensus model TVCN and is north of the corrected-consensus models FSSE and HCCA since the bulk of the NHC model guidance lies north of those latter two models. The upper-level environment is expected to improve to significantly during the next 12 h and beyond with the current 20 kt of southwesterly shear forecast to give way to shear of less than 10 kt. By 72 h and beyond, light shear from the southeast and east along with the development of strong upper-level outflow jets to the north of Florence is expected to create an environment that favors significant and possibly even rapid strengthening. The new NHC intensity forecast has been increased over the previous advisory in anticipation of these very favorable dynamical conditions developing, and now shows Florence becoming a hurricane by Sunday and a major hurricane in 3 days, followed by additional strengthening over the very warm Atlantic waters of at least 29 deg C that are about 2 deg C above normal right now. The consensus models IVCN and HCCA were closely followed, which are a little below the FSSE model. Key Messages: 1. Regardless of Florence's eventual track, large swells are affecting Bermuda and will begin to affect portions of the U.S. East Coast this weekend, resulting in life-threatening surf and rip currents. 2. The risk of other direct impacts associated with Florence along the U.S. East Coast next week has increased. However, there is still very large uncertainty in model forecasts of Florence's track beyond day 5, making it too soon to determine the exact location, magnitude, and timing of these impacts. Interests near and along the U.S. East Coast should monitor the progress of Florence through the weekend and ensure they have their hurricane plans in place. FORECAST POSITIONS AND MAX WINDS INIT 08/0900Z 24.5N 54.2W 55 KT 65 MPH 12H 08/1800Z 24.6N 55.0W 60 KT 70 MPH 24H 09/0600Z 24.6N 56.0W 65 KT 75 MPH 36H 09/1800Z 24.6N 57.2W 75 KT 85 MPH 48H 10/0600Z 24.9N 59.0W 90 KT 105 MPH 72H 11/0600Z 26.0N 64.0W 105 KT 120 MPH 96H 12/0600Z 28.0N 70.2W 120 KT 140 MPH 120H 13/0600Z 30.9N 75.8W 125 KT 145 MPH $$ Forecaster Stewart
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Hurricane Olivia Forecast Discussion Number 30
2018-09-08 04:56:31| Tropical Depression LIDIA
Issued at 800 PM PDT Fri Sep 07 2018
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Tropical Depression Nine Forecast Discussion Number 2
2018-09-08 04:55:35| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Fri Sep 07 2018 720 WTNT44 KNHC 080255 TCDAT4 Tropical Depression Nine Discussion Number 2 NWS National Hurricane Center Miami FL AL092018 1100 PM AST Fri Sep 07 2018 The depression continues to be impeded by moderate easterly shear with the center of circulation decoupled to the east of a deep convective banding feature. The initial intensity is held at 30 kt based on subjective intensity estimates from TAFB and SAB. The dynamical-statistical intensity guidance, as well as the large-scale models, indicate that the shear should diminish to less than 10 kt within the next 24 hours. A more favorable upper-wind pattern along with warm oceanic temperatures is expected to promote steady strengthening commencing after that time. The intensity forecast is based on a blend of the IVCN and the HCCA consensus models and remains below the stronger HWRF at days 4 and 5. The depression has been meandering during the past several hours, as a result of weak low- to mid-level steering currents created by a deep-layer trough digging southward over the eastern Atlantic. In 12 to 24 hours, a westward motion with a gradual increase in forward speed is forecast thereafter as the trough lifts northeast, and the subtropical ridge re-establishes to the north of the cyclone. The NHC track forecast lies closest to the HCCA and TVCN guidance and takes the system toward the Lesser Antilles by the end of the forecast period. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 13.9N 34.9W 30 KT 35 MPH 12H 08/1200Z 14.1N 35.6W 35 KT 40 MPH 24H 09/0000Z 14.2N 36.7W 35 KT 40 MPH 36H 09/1200Z 14.3N 38.4W 45 KT 50 MPH 48H 10/0000Z 14.4N 40.4W 55 KT 65 MPH 72H 11/0000Z 14.4N 45.2W 75 KT 85 MPH 96H 12/0000Z 14.4N 50.2W 80 KT 90 MPH 120H 13/0000Z 14.9N 56.2W 85 KT 100 MPH $$ Forecaster Roberts
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