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Tropical Storm Gordon Forecast Discussion Number 9
2018-09-04 16:50:29| National Hurricane Center (Atlantic)
Issued at 1000 AM CDT Tue Sep 04 2018 541 WTNT42 KNHC 041450 TCDAT2 Tropical Storm Gordon Discussion Number 9 NWS National Hurricane Center Miami FL AL072018 1000 AM CDT Tue Sep 04 2018 After an earlier disruption of the inner-core convection due to some southerly wind shear, Gordon has since developed a band of deep convection very near the well-defined center noted in both NOAA GOES-16 high-resolution satellite imagery and coastal NOAA WSR-88D Doppler radars. In addition, there has been a significant increase in lightning activity during the past couple of hours in the inner core, and Doppler radar velocities have increased to more than 45 kt at 25,000 ft in the band of convection near the center. NOAA and Air Force Reserve reconnaissance aircraft further indicate that Gordon has maintained a small radius of maximum winds (RMW) of 10-15 nmi, and that SFMR surface winds of 53-55 kt exist in the northeastern quadrant. These data support an intensity of 55 kt. The initial motion estimate is now toward the northwest at a slightly slower forward, or 305/13 kt. There is basically no change to the previous NHC forecast track reasoning. Reconnaissance fixes continue to fall along the previous forecast track, and the latest model guidance remains tightly packed and on top of the previous NHC forecast. As a result, there is high confidence that Gordon will make landfall along the north-central Gulf of Mexico coast in about 18 hours. After landfall, steering currents are forecast to weaken, resulting in Gordon slowing down considerably, which will enhance the heavy rainfall potential. By Friday, an approaching cold front and associated mid-/upper-level trough are expected to break down the subtropical ridge, allowing Gordon to turn northward and eventually turn northeastward on Saturday and merge with the cold front. The new official track forecast is near the model consensus and essentially on top of the previous NHC track. The aforementioned inner-core changes that have been occurring could be a harbinger that Gordon is finally starting to intensify. Intense lightning activity inside the small RMW is an indication of strong updrafts, which can enhance the strengthening process. Although the GFS and ECMWF models continue to forecast northwesterly shear of 10-15 kt, the explicit upper-level wind fields in the GFS, ECMWF, and UKMET models indicate that the 200-mb flow is forecast to become southeasterly and diffluent across Gordon in the next 12 h or so, which would act to enhance the development of inner-core convection. As result, the official intensity forecast maintains continuity and shows Gordon becoming a hurricane before landfall, which is above the guidance through that time. Once Gordon moves inland, the small circulation should spin down fairly quickly, and that portion of the forecast closely follows the various consensus-model intensity guidance. By 120 h, Gordon's circulation is expected to merge with a cold front over the Mississippi Valley region. 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. 2. Heavy rainfall from Gordon will affect the western Florida Panhandle, southwest Alabama, southern and central Mississippi, much of eastern 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 04/1500Z 28.5N 86.8W 55 KT 65 MPH 12H 05/0000Z 29.8N 88.5W 65 KT 75 MPH 24H 05/1200Z 31.5N 90.2W 35 KT 40 MPH...INLAND 36H 06/0000Z 32.8N 91.6W 25 KT 30 MPH...INLAND 48H 06/1200Z 33.7N 92.7W 20 KT 25 MPH...INLAND 72H 07/1200Z 35.4N 94.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 08/1200Z 37.7N 93.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 09/1200Z 40.9N 90.7W 20 KT 25 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart
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Hurricane Olivia Forecast Discussion Number 15
2018-09-04 16:41:02| Tropical Depression LIDIA
Issued at 800 AM PDT Tue Sep 04 2018
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Hurricane Florence Forecast Discussion Number 21
2018-09-04 16:37:32| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Tue Sep 04 2018 386 WTNT41 KNHC 041437 TCDAT1 Hurricane Florence Discussion Number 21 NWS National Hurricane Center Miami FL AL062018 1100 AM AST Tue Sep 04 2018 Florence's structure has gradually increased in organization, with SSMIS passes from a few hours ago revealing the development of a mid-level microwave eye. Dvorak estimates have responded in kind--TAFB is up to T4.0, SAB is at T4.5, and the objective ADT is in between at T4.4. Since there still appears to be moderate southwesterly shear inducing some tilt to the cyclone and disrupting the infrared satellite pattern, the initial intensity is raised conservatively to 65 kt, making Florence a hurricane. The current motion remains west-northwestward, or 295/10 kt, with Florence positioned near the southwestern edge of the subtropical ridge. The steering pattern ahead of Florence is rather complicated and will be evolving over the next few days. A large and complex mid-/upper-level trough located northeast of the Leeward Islands is expected to give way to the development of two upper-level highs centered near the Greater Antilles and southwest of the Azores, with Florence slowing down and turning northwestward between these new features. Despite this complex pattern, the spread in the track models is less than normal, which increases the confidence in the NHC track forecast for the next 5 days. There is some spread which begins to develop around day 5, with the ECMWF model moving Florence a little faster toward the north while the GFS maintains a slower speed and keeps the system to the south. The updated NHC track forecast has been nudged slightly to the east of the previous forecast on days 4 and 5, close to the TVCX consensus but not as far as the HCCA and ECMWF models. There is still too much model spread after day 5 to speculate what Florence might do beyond the official forecast period. Despite Florence becoming a hurricane, the southwesterly shear affecting the cyclone is expected to increase over the next day or two, which should prevent further intensification. In fact, the increasing shear, as well as mid-level relative humidities below 50 percent, should cause weakening between 24 and 72 hours. After 72 hours, decreasing shear and warmer sea surface temperatures should foster some re-intensification, with Florence expected to reattain hurricane intensity by day 5. The intensity guidance is in good agreement, and the NHC forecast is very close to a blend of HCCA, the Florida State Superensemble, and the ICON consensus. FORECAST POSITIONS AND MAX WINDS INIT 04/1500Z 19.7N 42.5W 65 KT 75 MPH 12H 05/0000Z 20.3N 44.0W 65 KT 75 MPH 24H 05/1200Z 21.3N 46.2W 65 KT 75 MPH 36H 06/0000Z 22.4N 48.2W 60 KT 70 MPH 48H 06/1200Z 23.6N 50.0W 55 KT 65 MPH 72H 07/1200Z 25.6N 52.7W 50 KT 60 MPH 96H 08/1200Z 27.5N 55.0W 55 KT 65 MPH 120H 09/1200Z 29.5N 56.5W 65 KT 75 MPH $$ Forecaster Berg
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Tropical Storm Gordon Forecast Discussion Number 8
2018-09-04 10:47:32| National Hurricane Center (Atlantic)
Issued at 400 AM CDT Tue Sep 04 2018 696 WTNT42 KNHC 040847 TCDAT2 Tropical Storm Gordon Discussion Number 8 NWS National Hurricane Center Miami FL AL072018 400 AM CDT Tue Sep 04 2018 Gordon has changed little in organization on geostationary satellite images or on the WSR-88D radar presentation over the past several hours. The storm has a small CDO with convective banding features primarily over the eastern semicircle of the circulation. Overall the cloud pattern is indicative of moderate westerly shear over the system, likely associated with an upper-level trough near the central Gulf of Mexico. An Air Force Reserve Unit Hurricane Hunter aircraft investigated Gordon a few hours ago and reported maximum SFMR-measured surface winds of 54 kt. On this basis the intensity had been adjusted to 55 kt, which is somewhat above the latest Dvorak estimates. It is assumed that the shear will not be strong enough to inhibit at least some strengthening before landfall, so the tropical cyclone is still forecast to become a hurricane later today. The official forecast, prior to landfall, is close to the latest LGEM intensity guidance, and near the upper end of the guidance suite. Gordon should weaken rapidly after landfall in the lower Mississippi Valley region. The motion continues west-northwestward, or 300/15 kt. There is little or no change to the NHC track prediction or forecast reasoning from the previous advisory. Gordon is expected to move along the southwestern periphery of a mid-level high pressure area and make landfall along the north-central Gulf of Mexico coast within 24 hours. After landfall, the cyclone is forecast to move northwestward, along the western side of the high, at a reduced forward speed. Late in the forecast period Gordon, or its post-tropical remnant, should turn northward to north-northeastward as it approaches the mid-latitude westerlies. The official track forecast is near the model consensus and very close to the previous NHC track. 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 this afternoon. 2. Heavy rainfall from Gordon will affect the western Florida Panhandle, southern Alabama, southern Mississippi and Louisiana, where totals could reach as high as 12 inches. This rainfall could cause flash flooding. FORECAST POSITIONS AND MAX WINDS INIT 04/0900Z 27.7N 85.7W 55 KT 65 MPH 12H 04/1800Z 29.0N 87.5W 65 KT 75 MPH 24H 05/0600Z 30.7N 89.6W 55 KT 65 MPH...INLAND 36H 05/1800Z 32.2N 91.0W 35 KT 40 MPH...INLAND 48H 06/0600Z 33.4N 92.3W 25 KT 30 MPH...INLAND 72H 07/0600Z 34.9N 94.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 08/0600Z 37.0N 94.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 09/0600Z 40.0N 92.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Pasch
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Hurricane Olivia Forecast Discussion Number 14
2018-09-04 10:45:30| Tropical Depression LIDIA
Issued at 200 AM PDT Tue Sep 04 2018
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