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| #897766 (Received by flhurricane at: 5:03 AM 08.Aug.2017) TCDAT2 Tropical Storm Franklin Discussion Number 7 NWS National Hurricane Center Miami FL AL072017 400 AM CDT Tue Aug 08 2017 The Belize Doppler weather radar indicates that Franklin`s inner-core circulation has tightened up considerably since the previous advisory, likely due to frictional convergence, and that a 10-15-nmi-diameter closed eye has developed. Radar reflectivity values have been steadily increasing in the eyewall, and this development trend is supported by infrared satellite imagery, which shows deep convection with cloud tops of -75C to -80C now completely covering the radar eye. The initial intensity is lowered to 45 kt for this advisory based on a typical decay rate for landfalling tropical cyclones. The initial motion estimate is 290/12 kt, based primarily on radar data. A deep-layer subtropical ridge that currently extends across the northern and central Gulf of Mexico is expected to remain intact through the forecast period, building slightly southward by 48 h and beyond. This entrenched steering pattern is expected to keep Franklin moving west-northwestward across the Yucatan peninsula the next 24 h or so, followed by westward motion across the Bay of Campeche until landfall occurs in 48-60 h. NHC model guidance remains in good agreement on this track scenario, and only a slight nudge to the south of the previous forecast track was required due to the more southward initial position of Franklin. Additional weakening is expected while Franklin moves across the Yucatan peninsula during the next 15 h or so. The recent inner-core structural improvements are expected to remain in place by the time the cyclone emerges over the warm waters of the Bay of Campeche. That, combined with low vertical shear values and a well-established outflow pattern, will allow for restrengthening to occur by Wednesday, possibly resulting in Franklin achieving hurricane status around 36-42 h. However, the GFS and ECMWF models are still forecasting significant northerly vertical shear near 20 kt to develop by 36 h and beyond, which could cap the intensification process or possibly even induce some weakening since mid-level dry air entrainment will accompany the northerly shear. However, since Franklin is expected to be near hurricane strength at landfall, a Hurricane Watch for mainland Mexico is warranted. The new NHC intensity forecast is similar to the previous advisory, and closely follows a blend of the HCCA and IVCN intensity consensus models. FORECAST POSITIONS AND MAX WINDS INIT 08/0900Z 19.3N 88.5W 45 KT 50 MPH...INLAND 12H 08/1800Z 19.7N 90.2W 35 KT 40 MPH...INLAND 24H 09/0600Z 20.1N 92.4W 50 KT 60 MPH...OVER WATER 36H 09/1800Z 20.3N 94.4W 60 KT 70 MPH 48H 10/0600Z 20.2N 96.6W 60 KT 70 MPH 72H 11/0600Z 19.7N 101.8W 20 KT 25 MPH...INLAND 96H 12/0600Z...DISSIPATED $$ Forecaster Stewart |
