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Tropical Storm Chris Forecast Discussion Number 13
2018-07-09 22:52:51| National Hurricane Center (Atlantic)
Issued at 500 PM EDT Mon Jul 09 2018 000 WTNT43 KNHC 092052 TCDAT3 Tropical Storm Chris Discussion Number 13 NWS National Hurricane Center Miami FL AL032018 500 PM EDT Mon Jul 09 2018 Satellite, Doppler radar, and Air Force reconnaissance aircraft data this afternoon indicate that inner-core region of Chris has improved in organization, and that the cyclone has strengthened some. A peak 850-mb flight-level of 73 kt was measured in the southwestern quadrant along with slightly rain-contaminated SFMR surface winds of 53-59 kt. The central pressure has also decreased to 997-996 mb. Based on these data, the intensity has been increased to 60 kt for this advisory. NOAA and Air Force Reserve reconnaissance fixes thus far today indicate that Chris has essentially remained nearly stationary for the past 9 hours. Steering should remain weak for the next 24 hours or so due to the cyclone being trapped in a large break in the subtropical ridge, thus little motion is expected. However, by 36 hours and beyond, a deepening mid-latitude trough along the U.S. Northeast and mid-Atlantic coasts is forecast to gradually lift out Chris to the northeast, with more significant northeastward acceleration occurring by 72 hours and beyond. Chris is expected to move across the offshore waters of Atlantic Canada on days 4 and 5 as a powerful extratropical low, possibly passing over southeastern Newfoundland around the 96-hour time period. The NHC model guidance continues to show fairly significant along-track or speed differences. As a result, the official forecast track remains close to the consensus track models TVCN, HCCA, and FSSE. A band of very dry mid-level air with humidity values less than 45 percent has completely encircled Chris, and the cyclone is beginning to take on the appearance of an annular formed hurricane with a new 15-nmi-diameter, cloud-filled eye having within the central convective cloud mass during the past couple of hours. The well-defined inner-core wind field, in conjunction with the with SSTs near 28 deg C and a low vertical wind shear regime, should act to maintain inner-core convective development. The result should be gradual strengthening over the next day or, with Chris becoming a hurricane later tonight or Tuesday morning and reaching a peak intensity of 80 kt by 36 hours. Gradual weakening should commence by 48 hours when the cyclone will be moving over cooler water and southwesterly wind shear begins to increase to near 20 kt. By 72 hours and beyond, Chris will be over SSTs less than 20 deg C and within stronger shear environment ahead of an approaching deep-layer trough, which will induce a rapid transition to a powerful extratropical cyclone before the system approaches Newfoundland in about 96 hours. The extratropical low is forecast to merge with a cold front in 96-120 hours, which should enhance the extratropical transition process. The new NHC intensity forecast is just an update of previous two advisories, and similar to the intensity model FSSE, which is sightly higher than the HCCA and IVCN intensity consensus models. FORECAST POSITIONS AND MAX WINDS INIT 09/2100Z 32.2N 74.4W 60 KT 70 MPH 12H 10/0600Z 32.3N 74.3W 65 KT 75 MPH 24H 10/1800Z 32.8N 73.6W 75 KT 85 MPH 36H 11/0600Z 34.0N 71.9W 80 KT 90 MPH 48H 11/1800Z 36.1N 69.0W 75 KT 85 MPH 72H 12/1800Z 42.2N 61.5W 65 KT 75 MPH...POST-TROP/EXTRATROP 96H 13/1800Z 48.3N 50.7W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 14/1800Z 52.0N 35.0W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart
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