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Potential Tropical Cyclone Three Forecast Discussion Number 2
2017-06-20 04:40:54| National Hurricane Center (Atlantic)
Issued at 1000 PM CDT Mon Jun 19 2017 000 WTNT43 KNHC 200240 TCDAT3 Potential Tropical Cyclone Three Discussion Number 2 NWS National Hurricane Center Miami FL AL032017 1000 PM CDT Mon Jun 19 2017 Earlier this afternoon, an Air Force Reserve reconnaissance aircraft investigating the central Gulf of Mexico disturbance found that the multiple swirls that this system possessed had consolidated into a single low-level circulation center with a pressure of about 1000 mb. However, since the circulation was and still is elongated north-to-south, the large low pressure system is being maintained as a potential tropical cyclone for this advisory cycle. The NWS now has the option to issue advisories, watches, and warnings for disturbances that are not yet a tropical cyclone, but which pose the threat of bringing tropical storm or hurricane conditions to land areas within 48 hours. Under previous policy this was not possible. These systems are known as Potential Tropical Cyclones in advisory products and are numbered from the same list as depressions. Because of the threat to the central Gulf coast, advisories have been initiated on Potential Tropical Cyclone Three and the appropriate watches/warnings have been issued. Users should be aware that forecast uncertainty for disturbances is generally larger than for tropical cyclones, especially beyond 48-72 hours. After stalling this afternoon due to re-organization of the system's center, the low now appears to be moving 330/07 kt based on recent conventional and microwave satellite fixes. The new forecast track has been shifted to the west of the previous advisory track through 48 hours, mainly due to the more westward initial position. Otherwise, no other significant changes were made to the previous forecast track. The low is expected to move generally northwestward through 48 hours around the southwestern portion of a deep-layer ridge located over the western Atlantic and Florida. After that, the system is forecast to turn northward around the ridge axis, moving into the south-central United States. The new NHC track forecast is a little to the right of the consensus model TVCA. Given the still disorganized nature of the circulation, and the fact that the wind and rain hazards extend well north and east of the center, users are encouraged to not focus on the details of the track forecast. The initial intensity remains 35 kt based on reconnaissance wind data and observations from nearby ships 3ETA7 and 3FZO8. Only slight strengthening is expected for the next 36 hours or so due to moderate to strong southwesterly vertical wind shear of 25-30 kt. By 48 hours, the shear is forecast to decrease to 20 kt or less, but the system will already be close to land at that time and probably not be able to take advantage of the lower shear conditions. The NHC intensity forecast is similar to the previous advisory and the intensity consensus model IVCN. The primary hazard from this disturbance is expected to be heavy rainfall over portions of the central and eastern Gulf Coast. FORECAST POSITIONS AND MAX WINDS INIT 20/0300Z 24.4N 89.5W 35 KT 40 MPH...POTENTIAL TROP CYCLONE 12H 20/1200Z 25.4N 90.3W 35 KT 40 MPH...TROPICAL CYCLONE 24H 21/0000Z 26.4N 91.3W 40 KT 45 MPH 36H 21/1200Z 27.1N 92.1W 40 KT 45 MPH 48H 22/0000Z 28.3N 92.8W 40 KT 45 MPH 72H 23/0000Z 31.8N 93.1W 25 KT 30 MPH...INLAND 96H 24/0000Z 35.2N 90.1W 20 KT 25 MPH...POST-TROP/INLAND 120H 25/0000Z...DISSIPATED INLAND $$ Forecaster Stewart
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