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Chill falls over the Atlantic as the official season heads towards close
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| #1004049 (Received by flhurricane at: 10:57 AM 07.Jun.2020) TCDAT3 Tropical Storm Cristobal Discussion Number 24 NWS National Hurricane Center Miami FL AL032020 1000 AM CDT Sun Jun 07 2020 Cristobal`s inner-core remains disorganized as multiple low-level circulations are seen rotating around the mean center used in the advisory. A large swirl just west of the alleged center has been dropping southward, and this could become a new center of circulation later today. Since the previous advisory, Cristobal`s overall appearance in satellite imagery has started to look more like a tropical cyclone with several small curved convective bands developing, especially in the eastern semicircle, along with some anticyclonic cirrus outflow noted. NOAA Doppler radar have indicated average velocities of 55-58 kt between 5000-8000 ft over the Chandeleur Sound, which equates to 45-48 kt surface winds in the northeastern quadrant. Also, an earlier Air Force Reserve reconnaissance mission sampled a long fetch of 55-59 kt at 925 mb in the southeastern quadrant, which equates to 41-44 kt surface winds. Therefore, the initial intensity is being held at 45 kt for this advisory, which is consistent with satellite intensity estimates of 45 kt from both TAFB and UW-CIMSS ADT. The initial motion is an uncertain 355/10 kt due to the uncertainty in the center position. Due to the broad inner-core wind field, there may be some erratic motion for the next 6 hours or so. Otherwise, the models remain in very good agreement in Cristobal turning north-northwestward later today. That motion is expected to continue until the 36-h period as the cyclone rounds the western periphery of a deep-layer ridged parked over the southeastern U.S. and Tennessee Valley area. By 48 hours and beyond, the ridge is forecast to slide eastward, allowing Cristobal to turn toward the north on day 2, and then move northeastward on days 3 and 4. A merger with an extratropical cyclone over the Great Lakes area is expected by day 5. The new NHC forecast track is similar to the previous advisory track, and lies close to the tightly packed consensus models. The continued broad structure of Cristobal and significant dry air entrainment should prevent any significant intensification before landfall, and the current intensity forecast holds the intensity constant at 45 kt through 12 h. Although the center is expected to be inland at that time, the long southerly wind fetch on the east side could keep winds to 45 kt over the Chandeleur Sound, near the coast of Mississippi and Alabama, and possibly over the inland lakes of southeastern Louisiana. Gradual weakening is forecast after landfall, with Cristobal weakening below tropical-storm strength by the 24-h time period. The new intensity forecast is similar to the previous advisory, and continues to show some slight re-intensification after the cyclone becomes extratropical at 72-96 hours, which is in agreement with the global model guidance. Cristobal remains a broad and asymmetric storm. Therefore, one should not focus on the exact forecast track, since the associated winds, storm surge, and rainfall extend well away the center. Key Messages: 1. There is a danger of life-threatening storm surge outside of the Hurricane and Storm Damage Risk Reduction System from the Mouth of the Mississippi River to Ocean Springs, Mississippi, and a Storm Surge Warning is in effect for those areas. Life-threatening storm surge remains possible in other portions of southern and southeastern Louisiana where a Storm Surge Watch is in effect. Residents in these locations should follow advice given by local emergency officials. 2. Tropical storm force winds should spread along the northern Gulf coast from central Louisiana to the western Florida Panhandle, including metropolitan New Orleans today, and a Tropical Storm Warning is in effect for this area. These winds will arrive well in advance of and extend well east of Cristobals center. 3. Heavy rainfall will continue across north Florida this morning, spreading from east to west across the eastern and central Gulf Coast from the Florida Panhandle into Louisiana today. The Central Gulf Coast region will be most prone to issues after the passage of the center of Cristobal from Sunday night into Monday. This heavy rain will move up the Lower and Mid Mississippi Valley Monday into Tuesday, then across the Upper Mississippi Valley and Northern Plains Tuesday and Tuesday night. Flash flooding, and new and renewed significant river flooding is possible, especially where heavier rainfall occurs over portions of the Gulf Coast through the Mississippi Valley. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 28.7N 90.0W 45 KT 50 MPH 12H 08/0000Z 30.2N 90.5W 45 KT 50 MPH...INLAND 24H 08/1200Z 32.6N 91.6W 30 KT 35 MPH...INLAND 36H 09/0000Z 35.2N 92.2W 25 KT 30 MPH...INLAND 48H 09/1200Z 38.9N 91.6W 25 KT 30 MPH...INLAND 60H 10/0000Z 43.5N 89.6W 25 KT 30 MPH...INLAND 72H 10/1200Z 47.8N 87.1W 30 KT 35 MPH...POST-TROP/EXTRATROP 96H 11/1200Z 52.6N 83.1W 30 KT 35 MPH...POST-TROP/EXTRATROP 120H 12/1200Z...DISSIPATED $$ Forecaster Stewart |
