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Tropical Storm Florence Forecast Discussion Number 20
2018-09-04 10:38:28| National Hurricane Center (Atlantic)
Issued at 500 AM AST Tue Sep 04 2018 770 WTNT41 KNHC 040838 TCDAT1 Tropical Storm Florence Discussion Number 20 NWS National Hurricane Center Miami FL AL062018 500 AM AST Tue Sep 04 2018 Florence's cloud pattern has changed very little during the past several hours, with the exception of a possible small Central Dense Overcast developing just to the east of the center. An earlier AMSR2 overpass revealed a rather obvious tilt toward the east-northeast, indicative of the moderate southwesterly shear. The initial intensity is held a 60 kt, and is supported by the Dvorak subjective and objective T-numbers. Florence should exhibit little change in strength during the next 24 hours or so, as the cyclone traverses marginally warm sea surface temperatures and is influenced by modest west-southwesterly shear. Slight weakening is expected during the mid- forecast period as the shear gradually increases with time. Afterward, the upper-level wind environment should become a little more favorable and, at the same time, Florence will be moving back over warmer SSTs. Consequently, the cyclone should gradually strengthen through day 5. This forecast is unchanged from the previous one, and is in good agreement with the NOAA-HCCA guidance. The initial motion estimate is west-northwestward, or 290/11 kt. The cyclone is expected to be steered west-northwestward for the next 48 hours by a mid- to upper tropospheric ridge anchored to the north, followed by a northwestward turn around the 72 hr period as it enters a growing weakness in the aforementioned ridge. A rather large spread in the global and hurricane models remains particularly beyond day 4, however, the consensus models and the global ensemble means have have been fairly consistent from run to run. This forecast is just a bit to the north of the previous advisory and just south of the consensus models. FORECAST POSITIONS AND MAX WINDS INIT 04/0900Z 19.3N 42.0W 60 KT 70 MPH 12H 04/1800Z 19.9N 43.7W 60 KT 70 MPH 24H 05/0600Z 20.8N 45.8W 60 KT 70 MPH 36H 05/1800Z 21.8N 48.0W 55 KT 65 MPH 48H 06/0600Z 22.9N 50.2W 50 KT 60 MPH 72H 07/0600Z 25.2N 53.4W 50 KT 60 MPH 96H 08/0600Z 27.1N 55.6W 55 KT 65 MPH 120H 09/0600Z 29.1N 57.7W 65 KT 75 MPH $$ Forecaster Roberts
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Tropical Storm Gordon Forecast Discussion Number 7
2018-09-04 04:47:28| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Mon Sep 03 2018 713 WTNT42 KNHC 040247 TCDAT2 Tropical Storm Gordon Discussion Number 7 NWS National Hurricane Center Miami FL AL072018 1100 PM EDT Mon Sep 03 2018 WSR-88D radar data from Tampa shows that the small inner core of Gordon has lost some organization during the past few hours, and GOES-16 satellite imagery and recent aircraft fixes indicate that the low-level center is located near the southwestern edge of the main convective mass. This suggests that there may be some light to moderate westerly shear affecting the cyclone. The Air Force Reserve reconnaissance aircraft recently measured peak 850-mb flight-level winds of 57 kt, and SFMR winds of 50-55 kt. A blend of these data yields an initial wind speed estimate of 50 kt. A UW/CIMSS shear analysis and the SHIPS model indicates that there is about 10-15 kt of westerly shear over the system. The SHIPS guidance shows a slight relaxation of the shear during the next 12-18 hours while the system moves over the warm waters of the Gulf of Mexico, which should allow for some strengthening. However, Gordon is a small tropical cyclone and subtle changes in shear (both up and down) can result in fairly quick intensity changes for systems like this. The NHC intensity forecast assumes that shear will not be prohibitive and that Gordon will become a hurricane before reaching the northern Gulf coast. The NHC intensity forecast is close to the SHIPS guidance through 24 hours, then follows the HFIP corrected consensus after landfall which shows Gordon weakening rapidly over land. Gordon is moving west-northwestward at about 15 kt. The tropical storm is expected to maintain a west-northwestward to northwestward heading during the next few days while it moves around the southwestern portion of a large deep-layer ridge centered over the Mid-Atlantic states. After that time, the cyclone should decelerate as it moves around the western periphery of the ridge. The track guidance continues to be tightly clustered through 72 h, and no significant changes were required to the previous NHC track forecast. 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. Residents in these areas should listen to advice from their local officials. All preparations to protect life and property should be rushed to completion, as tropical storm conditions are expected to arrive in the warning areas Tuesday afternoon. 2. Heavy rainfall from Gordon will affect southern Alabama, southern Mississippi and Louisiana, where totals could reach as high as 8 inches. This rainfall could cause flash flooding. FORECAST POSITIONS AND MAX WINDS INIT 04/0300Z 26.9N 84.3W 50 KT 60 MPH 12H 04/1200Z 28.3N 86.3W 55 KT 65 MPH 24H 05/0000Z 30.0N 88.6W 65 KT 75 MPH 36H 05/1200Z 31.6N 90.3W 40 KT 45 MPH...INLAND 48H 06/0000Z 32.9N 91.6W 25 KT 30 MPH...INLAND 72H 07/0000Z 34.6N 93.9W 20 KT 25 MPH...INLAND 96H 08/0000Z 36.5N 94.9W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 09/0000Z 39.5N 93.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown
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Hurricane Norman Forecast Discussion Number 28
2018-09-04 04:35:30| National Hurricane Center (East Pacific)
Issued at 800 PM PDT Mon Sep 03 2018 095 WTPZ41 KNHC 040235 TCDEP1 Hurricane Norman Discussion Number 28 NWS National Hurricane Center Miami FL EP162018 800 PM PDT Mon Sep 03 2018 Norman continues to slowly weaken. Satellite images indicate that the banding features are not as well organized as they were earlier today, and the cloud tops have warmed some during the past few hours. The Dvorak classifications have decreased, and a blend of the latest estimates supports lowering the initial intensity to 80 kt. Norman continues to move quickly westward at 18 kt steered by a strong subtropical ridge to its north-northeast. This general heading, but with a significant decrease in forward speed, is expected during the next day or two while Norman nears the edge of the ridge. Thereafter, a turn to the northwest and then north-northwest is expected while Norman moves around the ridge and toward a large deep-layer trough over the northern Pacific. There remains a fair amount of spread on where and when Norman makes the turn, but the guidance did not change much overall this cycle. Therefore, only small changes were made to the previous advisory, and this forecast lies close to the middle of the guidance envelope. Norman could weaken a little more overnight and on Tuesday, but the guidance shows the intensity flattening out in the 24- to 48-hour time period. After that time, however, a sharp increase in shear, cooler waters, and a drier air mass should cause more significant weakening. The NHC intensity forecast is largely an update of the previous one and in line with the IVCN and HCCA consensus models. Now that Norman has crossed into the central Pacific basin, future advisories on this system will be issued by the Central Pacific Hurricane Center. These forecasts can be found on the web at http://www.prh.noaa.gov/cphc. FORECAST POSITIONS AND MAX WINDS INIT 04/0300Z 19.8N 140.2W 80 KT 90 MPH 12H 04/1200Z 20.0N 142.5W 75 KT 85 MPH 24H 05/0000Z 20.1N 144.9W 70 KT 80 MPH 36H 05/1200Z 20.2N 147.0W 70 KT 80 MPH 48H 06/0000Z 20.6N 148.7W 70 KT 80 MPH 72H 07/0000Z 22.5N 151.1W 65 KT 75 MPH 96H 08/0000Z 25.3N 153.3W 50 KT 60 MPH 120H 09/0000Z 28.1N 155.2W 35 KT 40 MPH $$ Forecaster Cangialosi
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Tropical Storm Florence Forecast Discussion Number 19
2018-09-04 04:31:28| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Mon Sep 03 2018 605 WTNT41 KNHC 040231 TCDAT1 Tropical Storm Florence Discussion Number 19 NWS National Hurricane Center Miami FL AL062018 1100 PM AST Mon Sep 03 2018 Although Florence continues to produce a fairly circular area of deep convection, microwave images have revealed that there is a significant southwest-to-northeast vertical tilt of the circulation due to southwesterly shear. The initial intensity is held at 60 kt, using a blend of the Dvorak CI-numbers from TAFB and SAB. This estimate is a little below the latest automated Dvorak values from CIMSS at the University of Wisconsin. The strong tropical storm is moving west-northwestward, or 285 degrees, at 12 kt steered by a subtropical ridge to its north. The storm is expected to gradually turn northwestward with a decrease in forward speed during the next several days as it moves toward a persistent weakness in the subtropical ridge. There remains a fair amount of spread in the guidance, especially in the 3- to 5-day time period, but the consensus aids have changed little this cycle. Therefore, no significant changes were made to the previous forecast, and this one lies near the middle of the guidance envelope. Little change in strength is expected through early Tuesday as Florence remains over marginally warm waters and in moderate wind shear conditions. Slight weakening is expected during the middle part of the week due to a gradual increase in southwesterly or westerly shear. Beyond that time, however, the shear is expected to decrease and Florence will be over much warmer waters. Therefore, slow strengthening is shown at the end of the forecast period. This forecast is unchanged from the previous one, and is in good agreement with the HCCA guidance. The 34- and 50-kt initial wind radii have been expanded outward based on recent ASCAT passes. FORECAST POSITIONS AND MAX WINDS INIT 04/0300Z 18.9N 41.0W 60 KT 70 MPH 12H 04/1200Z 19.4N 42.7W 60 KT 70 MPH 24H 05/0000Z 20.1N 44.9W 55 KT 65 MPH 36H 05/1200Z 21.1N 47.2W 55 KT 65 MPH 48H 06/0000Z 22.1N 49.5W 50 KT 60 MPH 72H 07/0000Z 24.5N 53.1W 50 KT 60 MPH 96H 08/0000Z 26.8N 55.8W 55 KT 65 MPH 120H 09/0000Z 28.4N 57.8W 60 KT 70 MPH $$ Forecaster Cangialosi
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Tropical Storm Gordon Forecast Discussion Number 6
2018-09-03 22:52:24| National Hurricane Center (Atlantic)
Issued at 500 PM EDT Mon Sep 03 2018 249 WTNT42 KNHC 032052 TCDAT2 Tropical Storm Gordon Discussion Number 6 NWS National Hurricane Center Miami FL AL072018 500 PM EDT Mon Sep 03 2018 Data from an earlier Air Force Reserve reconnaissance mission, along with Doppler velocity data from the Miami radar, indicate that Gordon has strengthened a little more, with some these data supporting an intensity of about 50 kt. However, since the earlier 5-n mi-diameter eye has eroded and inner-core convection has become somewhat ragged, the initial intensity remains 45 kt. The initial motion estimate is 300/15 kt. The latest model guidance is still in excellent agreement on Gordon maintaining a west- northwestward to northwestward motion for the next 48-72 hours right up until landfall as a strong ridge to the north of the cyclone is forecast to remain locked in place over the southeastern U.S. and mid-Atlantic states. Although the guidance has shifted slightly back to the left, no appreciable changes were made to the previous forecast track since the models have been 'windshield-wipering' back and forth over the past 24 hours. The new NHC track forecast is similar to or a little north of the latest consensus models. Overall, Gordon's presentation in both radar and satellite imagery has steadily improved since the previous advisory. Although the inner-core structure has eroded somewhat, outer banding features have improved and now extend as far north as central and northern Florida. The GFS- and ECMWF-based SHIPS intensity models continue to indicate that westerly to northwesterly wind shear of 10-15 kt is expected to affect Gordon for the next 36 hours, a flow pattern that would generally hinder development. However, the global models' upper-level wind fields show Gordon remaining near or underneath a synoptic-scale upper-level anticyclone, a more favorable pattern that supports at least steady strengthening. Since Gordon will be moving over very warm sea-surface temperatures of about 30 C, the cyclone is forecast to reach hurricane strength in 24-36 hours, just before landfall. For that reason, a Hurricane Warning has been issued for portions of the central Gulf Coast. The NHC intensity forecast is a little above the previous advisory, and is close to a blend of the consensus models HCCA, FSSE, and IVCN. 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. Residents in these areas should listen to advice from their local officials. All preparations to protect life and property should be rushed to completion, as tropical storm conditions are expected to arrive in the warning areas Tuesday afternoon or evening. 2. Heavy rainfall from Gordon will affect southern Alabama, southern Mississippi and Louisiana, where totals could reach as high as 8 inches. This rainfall could cause flash flooding. 3. Rainfall will continue across portions of South Florida and the Florida Keys through early Tuesday, where totals could reach as high as 8 inches. FORECAST POSITIONS AND MAX WINDS INIT 03/2100Z 26.2N 82.6W 45 KT 50 MPH 12H 04/0600Z 27.3N 84.8W 50 KT 60 MPH 24H 04/1800Z 28.9N 87.2W 60 KT 70 MPH 36H 05/0600Z 30.6N 89.3W 65 KT 75 MPH...INLAND 48H 05/1800Z 32.1N 91.1W 35 KT 40 MPH...INLAND 72H 06/1800Z 34.1N 93.5W 25 KT 30 MPH...INLAND 96H 07/1800Z 35.5N 94.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 08/1800Z 38.2N 94.8W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Stewart
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