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Tropical Storm Franklin Forecast Discussion Number 3
2017-08-07 10:49:32| National Hurricane Center (Atlantic)
Issued at 500 AM EDT Mon Aug 07 2017 000 WTNT42 KNHC 070849 TCDAT2 Tropical Storm Franklin Discussion Number 3 NWS National Hurricane Center Miami FL AL072017 500 AM EDT Mon Aug 07 2017 Deep convection associated with Franklin has been steadily increasing in both coverage and vertical depth since the previous advisory. Wind data from a late-arriving 0231Z ASCAT-A pass suggest that Franklin might not have had a closed surface circulation at that time. However, the new GOES-16 nighttime microphysics imagery clearly shows low clouds moving from west to east on the south side of the alleged center, which is suggestive of a closed low-level circulation. The intensity has been nudged upward to 40 kt based on sustained winds of 39 kt measured at 4-meters elevation from NOAA buoy 42057 located about 110 nmi east of the center. The initial motion estimate is 300/12 kt. The latest NHC model guidance remains in excellent agreement that Franklin will continue to move west-northwestward along the south side of a deep-layer ridge during the next 48 hours or so, making landfall along the east coast of the Yucatan peninsula in 18-24 hours. After the cyclone crosses over Yucatan and moves into the Bay of Campeche by Wednesday, a more westward motion is expected thereafter as the ridge currently situated over northern Mexico and the southwestern U.S. builds southward. The track model guidance is tightly clustered around the previous forecast track, so the new forecast track is just an extension of the previous one and lies down the middle of the guidance envelope. Upper-level outflow continues to expand in the western semicircle, and a pronounced poleward outflow channel has developed in the northern semicircle, which is being aided by a large upper-level low located north of Puerto Rico. Although UW-CIMSS wind analyses indicate that modest westerly mid-level shear is still affecting the cyclone, that hindrance is forecast to abate in another 6 h or so. Both the GFS and ECMWF models are forecasting the deep-layer and mid-level shear to decrease to near zero in the 12-24 h period, suggesting that Franklin could undergo a period of rapid intensification right up until landfall occurs. Unfortunately, the official intensity forecast does not directly reflect that possible intensification trend due to the 24-h position being inland over Yucatan with weakening occuring at that time due to land interaction. Franklin is likely to reach a peak intensity of about 60 kt or so prior to landfall, and for that reason the government of Mexico has issued a Hurricane Watch. The cyclone will weaken some as it moves over the Yucatan, but re-strengthening is expected after Franklin emerges over the very warm waters of the Bay of Campeche in the 48-72 h period. The NHC intensity forecast remains close to the higher SHIPS guidance at 24 hours, and is near the IVCN and HCCA consensus models after that time. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 17.1N 84.2W 40 KT 45 MPH 12H 07/1800Z 18.0N 85.8W 50 KT 60 MPH 24H 08/0600Z 19.0N 88.0W 55 KT 65 MPH...INLAND 36H 08/1800Z 19.9N 90.2W 40 KT 45 MPH...INLAND 48H 09/0600Z 20.4N 92.3W 45 KT 50 MPH...OVER WATER 72H 10/0600Z 21.0N 96.4W 55 KT 65 MPH 96H 11/0600Z 21.1N 100.5W 25 KT 30 MPH...INLAND 120H 12/0600Z...DISSIPATED $$ Forecaster Stewart
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