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Tropical Storm Cristobal Forecast Discussion Number 25
2020-06-07 22:48:09| National Hurricane Center (Atlantic)
Issued at 400 PM CDT Sun Jun 07 2020 000 WTNT43 KNHC 072048 TCDAT3 Tropical Storm Cristobal Discussion Number 25 NWS National Hurricane Center Miami FL AL032020 400 PM CDT Sun Jun 07 2020 At least two low-level vortices have been noted rotating cyclonically within the broad inner-core circulation, with one swirl located southeast of the advisory position approaching the Mississippi Delta and the other swirl located inland to the northwest of Grand Isle, Louisiana. The larger swirl in the southeastern quadrant will likely become the dominant low-level circulation center later tonight after that feature moves inland and frictional convergence tightens up the broad inner-core wind field a little bit. The initial intensity remains 45 kt based on data from surface observations and NOAA Doppler radar velocity data from Slidell and Mobile, along with a satellite intensity estimate of T3.0/45 kt from TAFB. The initial motion estimate is an uncertain 355/06 kt due to the uncertainty in the center position. Some erratic motion will still be possible for the next 6-12 hours due to the dumb-belling motion of the multiple low-level circulations. Overall, however, the models remain in excellent agreement on Cristobal turning north-northwestward tonight and continuing that motion through 24 hours. By Monday night, a turn toward north is forecast, followed by a faster motion toward the northeast on Tuesday and Wednesday ahead of an approaching frontal system. The cyclone is expected to slow down on days 3 and 4 during extratropical transition. The new NHC forecast track is very similar to the previous track forecast, and lies down the center of the the tightly packed consensus models. No significant intensification is expected before landfall occurs late this afternoon or early evening primarily due to Cristobal's broad wind field. However, intrusions of dry air could result in wind gusts of 55-60 kt in some of the stronger squalls. After landfall, only slow weakening is expected due to the cyclone's large wind field. In the 60-96 hour period, some slight strengthening to gale-force strength is forecast due to strong baroclinic forcing during the extratropical transition, and a long southerly to south-southwesterly wind fetch blowing across Lake Michigan. The official intensity closely follows a blend of the GFS, UKMET, and ECMWF global models. 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 will continue to spread along the northern Gulf coast from central Louisiana to the western Florida Panhandle, including metropolitan New Orleans this evening, and a Tropical Storm Warning is in effect for this area. These winds will extend well east of Cristobals center. 3. Heavy rainfall will continue across north Florida into this evening, diminishing overnight. Heavy rain will continue to push inland across the central Gulf coast this afternoon and into the Lower Mississippi Valley tonight. The Central Gulf Coast region will be most prone to heavy rain issues after the passage of the center of Cristobal from tonight through 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 07/2100Z 29.1N 89.9W 45 KT 50 MPH 12H 08/0600Z 30.9N 90.8W 40 KT 45 MPH...INLAND 24H 08/1800Z 33.4N 91.6W 25 KT 30 MPH...INLAND 36H 09/0600Z 36.7N 91.7W 25 KT 30 MPH...INLAND 48H 09/1800Z 40.5N 90.6W 25 KT 30 MPH...INLAND 60H 10/0600Z 45.2N 88.3W 30 KT 35 MPH...INLAND 72H 10/1800Z 48.7N 85.8W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 11/1800Z 53.2N 81.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 12/1800Z...DISSIPATED $$ Forecaster Stewart
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