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| #800197 (Received by flhurricane at: 4:38 AM 02.Sep.2015) TCDAT1 TROPICAL STORM FRED DISCUSSION NUMBER 14 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062015 500 AM AST WED SEP 02 2015 Fred has been devoid of significant deep convection near the center for almost 6 hours. The pronounced upper-level circulation and associated convection is displaced at least 150 n mi to the east of the now fully exposed low-level circulation due to strong westerly vertical wind shear. The initial intensity of 40 kt is based on a gradual spin down of the 45-kt ASCAT-B vortex mentioned in the previous discussion, and a blend of 35-kt and 45-kt Dvorak satellite intensity estimates from SAB and TAFB, respectively. Now that the upper-level circulation has decoupled from the low- and mid-level circulations, it is unlikely that Fred will restrengthen since the cyclone will be moving over cooler SSTs of about 26 deg C, into even stronger shear in excess of 30 kt, and also into a much drier airmass. Cloud top temperatures in the radius of maximum winds are only in the -10 to -20 deg C range, which suggests that Fred's circulation now likely only extends no higher than the 400-mb level, if that. As a result, Fred should continue to slowly spin down and become a depression within the next 18-24 hours, and degenerate into a remnant low within 36 hours, if not sooner. The NHC intensity forecast follows a blend of the SHIPS, LGEM, and HWRF models, which steadily weaken Fred, and is lower than the IVCN model due to the GFDL model re-strengthening Fred into a 75-kt hurricane again, which has created a high bias in the consensus. The initial motion estimate is 295/09. There remains no significant change to the previous track forecast or reasoning. Fred is expected to continue moving west-northwestward for the next 72 hours or so while it remains embedded within the trade wind flow south of the Bermuda-Azores subtropical high. After that time, the models continue to forecast a mid-latitude trough to dig southward over the central Atlantic and erode the western portion of the ridge, allowing Fred to turn slowly northwestward by 96 hours and northward by 120 hours. The new forecast track is a tad south of the previous advisory track, mainly due to the more southerly initial position. The track forecast also lies along the southern edge of the guidance envelope and is left of the TVCA consensus model due to the more northerly track created by the much stronger and vertically deeper GFDL model, which has strongly biased the consensus model with a more northward and eastward track. FORECAST POSITIONS AND MAX WINDS INIT 02/0900Z 19.5N 30.1W 40 KT 45 MPH 12H 02/1800Z 20.0N 31.4W 35 KT 40 MPH 24H 03/0600Z 20.7N 32.9W 30 KT 35 MPH 36H 03/1800Z 21.2N 34.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 04/0600Z 21.6N 35.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 05/0600Z 22.3N 39.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 06/0600Z 23.5N 41.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 07/0600Z 25.6N 43.3W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Stewart |
