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Tropical Storm Chris Forecast Discussion Number 12
2018-07-09 16:55:49| National Hurricane Center (Atlantic)
Issued at 1100 AM EDT Mon Jul 09 2018 000 WTNT43 KNHC 091455 TCDAT3 Tropical Storm Chris Discussion Number 12 NWS National Hurricane Center Miami FL AL032018 1100 AM EDT Mon Jul 09 2018 A NOAA reconnaissance aircraft investigating Chris this morning has found little change in the overall structure of the cyclone. The peak 8000-ft wind measured was 60 kt to the south of the center along with a 51-kt SFMR surface wind. The minimum pressure has also remained steady at 999 mb during the entire mission which is still ongoing. Although an eye-like feature has briefly appeared in WSR-88D Doppler radar data from Morehead City and in satellite imagery as well, the convection surrounding that feature has been mostly shallow and ragged. Based on these data, the intensity remains at 50 kt for this advisory. Air Force and NOAA reconnaissance fixes the past several hours and satellite fixes indicate that Chris has moved little. Steering currents are forecast to remain weak for the next 24 hours or so, resulting in continued slow movement. By 36 hours, however, a shortwave trough is forecast to dig southeastward out of Canada and into the northeastern U.S. and mid-Atlantic states, which should help to eject the cyclone northeastward. By 48 hours and beyond, the shortwave trough will help to amplify a deep-layer trough near the U.S. east coast, causing Chris to accelerate northeastward toward the Atlantic Canada region. The NHC model guidance continues to show little cross-track differences, but fairly significant along-track or speed differences. As a result, the official forecast track remains close to the consensus track models. A narrow band of dry mid-level air has wrapped all the way around and into the inner-core region, which has caused some erosion of the associated convection, along with some upwelling. However, the reconnaissance wind data indicated that Chris has a relatively small radius of maximum winds (RMW) of 15 nmi to the south and about 25 nmi to the north. This well-defined inner-core wind field, coupled with warm water and low vertical shear conditions, should enable the cyclone to mix out the dry air later today and tonight, which will allow for strengthening to begin. The intensification process should be steady at a near-normal rate for the next 36 hours or so, followed by gradual weakening in a few days as the waters beneath Chris begin to cool and the wind shear increases from the southwest. By 72 hours and beyond, Chris will be over much colder water (SSTs less than 20 deg C) and within a high shear environment of 30 kt or more, which will induce a rapid transition to a powerful extratropical cyclone as the system approaches Newfoundland. The extratropical low is forecast to interact or merge with a strong cold front by 96 hours when the cyclone is near Newfoundland, which will enhance the extratropical transition process. The new intensity forecast is similar to the previous advisory and shows Chris reaching hurricane strength by Tuesday. Chris could reach a peak intensity of 80 kt between the 36 and 48 hour time periods before weakening begins shortly thereafter. FORECAST POSITIONS AND MAX WINDS INIT 09/1500Z 32.2N 74.5W 50 KT 60 MPH 12H 10/0000Z 32.3N 74.4W 55 KT 65 MPH 24H 10/1200Z 32.4N 74.3W 65 KT 75 MPH 36H 11/0000Z 33.3N 73.0W 75 KT 85 MPH 48H 11/1200Z 34.8N 70.9W 75 KT 85 MPH 72H 12/1200Z 40.5N 64.0W 70 KT 80 MPH 96H 13/1200Z 47.0N 55.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 14/1200Z 51.1N 41.0W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart
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