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| #932270 (Received by flhurricane at: 10:54 AM 10.Jul.2018) TCDAT3 Tropical Storm Chris Discussion Number 16 NWS National Hurricane Center Miami FL AL032018 1100 AM EDT Tue Jul 10 2018 During the past 6 hours, Chris has developed a well-defined eye in both satellite and radar imagery at times, with a diameter that has varied in size from 30 nmi to the present 20 nmi. The overall convective pattern has also become more symmetrical with well-established outflow present in all quadrants. Satellite intensity estimates are T3.5/55 kt from TAFB, and T4.0/65 kt from SAB and UW-CIMSS ADT, and Chris certainly has the satellite appearance of being a hurricane. However, the intensity is being maintained at 60 kt for this advisory due to significant cold upwelling that has occurred beneath the cyclone when Chris was moving slowly during the previous 48 hours. The colder waters have likely stabilized the boundary layer, which has inhibited stronger winds aloft from mixing down to the surface. The cold upwelling is supported by sea-surface temperature (SST) data from nearby NOAA Buoy 41002, which has shown 6 deg F of cooling during the past 48 hours, and is currently sitting at 76F. An Air Force Reserve reconnaissance aircraft is scheduled to investigate Chris this afternoon to provide a better intensity estimate. Recent satellite and radar fixes indicate that Chris is finally moving northeastward at a faster forward speed, and the initial motion estimate is now 050/08 kt. The narrow subtropical ridge to the southeast of the cyclone is getting pushed northward by the remnants of Beryl, which has helped to finally nudge Chris toward the northeast. A further increase in forward speed is expected as a strong deep-layer trough digs southeastward along the U.S. east coast, accelerating the cyclone at forward speeds of 25-30 kt by 48 hours and beyond. Chris is forecast to pass well southeast of Nova Scotia in a couple of days, and move near or over southeastern Newfoundland in about 60 hours. The NHC track guidance remains in good agreement on the evolving steering flow regime, but there continues to be some pronounced speed differences. The new NHC track forecast is similar to the previous advisory, and lies close to the consensus models HCCA, FSSE, and TVCN. My best estimate, based on the data from Buoy 41002, is that significant upwelling likely occurred within the 30-kt wind radii while Chris was nearly stationary. Assuming that that is the case, then Chris will be moving over warmer waters shortly, which should allow for an increase in convection to occur and also for winds aloft to better mix downward to the surface. The vertical wind shear is forecast to remain modest at 10-15 kt for the next 24 hours, so gradual intensification is expected during that time. By 48 hours, Chris will have crossed over the north wall of the Gulfstream and be moving over SSTs colder than 20 deg C, which will combine with strong southwesterly wind shear, and cause Chris to rapidly transition to an extratropical cyclone. The official intensity forecast follows the FSSE intensity model through 36 hours, and then shows more significant weakening after that, similar to the SHIPS, LGEM, and HCCA models. FORECAST POSITIONS AND MAX WINDS INIT 10/1500Z 33.1N 73.1W 60 KT 70 MPH 12H 11/0000Z 33.9N 71.9W 70 KT 80 MPH 24H 11/1200Z 35.6N 69.4W 75 KT 85 MPH 36H 12/0000Z 38.4N 65.5W 75 KT 85 MPH 48H 12/1200Z 42.0N 60.6W 65 KT 75 MPH 72H 13/1200Z 48.1N 49.3W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 14/1200Z 52.0N 31.9W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 15/1200Z 54.0N 18.0W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart |
