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Tropical Storm Ophelia Forecast Discussion Number 4
2017-10-10 04:52:23| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Mon Oct 09 2017 000 WTNT42 KNHC 100252 TCDAT2 Tropical Storm Ophelia Discussion Number 4 NWS National Hurricane Center Miami FL AL172017 1100 PM AST Mon Oct 09 2017 Ophelia's center is just south of a broad curved band of deep convection. At synoptic time, the subjective Dvorak classifications from TAFB and SAB were both at 2.5, or 35 kt, while the CIMSS SATCON was at 43 kt. Given the increasingly curved structure of the bands during the last couple of hours, the initial intensity is set at 45 kt, a bit higher than the previous advisory. While the tropical storm is fighting some moderate vertical shear currently, the global models suggest that this should lighten some between now and about day 4 as Ophelia resides between the mid-latitude and subtropical westerlies. Even though the system will be traversing cool 26C SSTs, upper-tropospheric temperatures likely will also be cool, allowing for deep convection to continue. The mid-level moisture analyzed in the SHIPS guidance appears to be somewhat dry, though the total precipitable water imagery shows distinct moistening near the system during the last couple of days. The official intensity forecast shows gradual intensification through day 3, then slow weakening thereafter. This is close to a blend of the LGEM statistical guidance and the HWRF dynamical model and is slightly above that of the previous advisory. The initial position has fairly small uncertainty as the low-level center is along the southern edge of the deep convection, as seen in the GOES-16 shortwave infrared imagery. Ophelia is moving toward the northeast at about 6 kt - somewhat unexpectedly - this evening. Despite this, the model guidance suggests that a ridge will soon build in strongly north of Ophelia and force the tropical storm to the southeast and then south during the next couple of days. Around day 3, Ophelia should get kicked out toward the east-northeast by an approaching trough in the mid-latitude westerlies. The official track forecast is north of the previous forecast in the short term and east-northeast in the long term, and is in between the HFIP Corrected Consensus Approach (HCCA) and the previous forecast. The initial tropical-storm-force wind radii was adjusted outward based upon a 2137Z AMSU size analysis. The official size forecast is based upon the RVCN consensus technique. FORECAST POSITIONS AND MAX WINDS INIT 10/0300Z 32.3N 39.0W 45 KT 50 MPH 12H 10/1200Z 32.5N 38.4W 50 KT 60 MPH 24H 11/0000Z 32.0N 38.1W 55 KT 65 MPH 36H 11/1200Z 31.1N 37.9W 65 KT 75 MPH 48H 12/0000Z 30.4N 37.5W 70 KT 80 MPH 72H 13/0000Z 30.8N 35.5W 75 KT 85 MPH 96H 14/0000Z 32.5N 32.0W 70 KT 80 MPH 120H 15/0000Z 34.5N 26.5W 60 KT 70 MPH $$ Forecaster Landsea
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