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Tropical Storm Humberto Forecast Discussion Number 12
2019-09-15 16:54:13| National Hurricane Center (Atlantic)
Issued at 1100 AM EDT Sun Sep 15 2019 000 WTNT44 KNHC 151454 TCDAT4 Tropical Storm Humberto Discussion Number 12 NWS National Hurricane Center Miami FL AL092019 1100 AM EDT Sun Sep 15 2019 Visible and passive microwave satellite imagery indicate that Humberto's inner-core region has improved markedly since early this morning, including the development of a small but ragged mid-level eye. In addition, significant dry air entrainment that has been plaguing the cyclone since its formation appears to have abated based on the recent development of deep convection in the dry slot located in the southern semicircle of Humberto's circulation. Anticyclonic outflow has also been increasing in all quadrants, along with a hint of cloud-filled eye in recent visible imagery. Buoy 41010 located just west of the center recently reported a pressure of 1001.8 mb and 41-kt winds at 4-meters elevation. The initial intensity has been increased to 55 kt based on a Dvorak intensity estimate of T3.5/55 kt from TAFB. AN Air Force Reserve reconnaissance aircraft will reconnoiter Humberto this afternoon, providing more detailed information on the cyclone's intensity. The initial motion estimate is 350/06 kt, based mainly on microwave satellite fix positions. NHC model guidance remains in excellent agreement on Humberto moving slowly northward through a break in the subtropical ridge today and tonight, then making a sharp turn toward the northeast on Monday when the cyclone passes north of the narrow east-west oriented ridge axis. On days 2-5, the tropical cyclone is forecast to gradually accelerate toward the northeast and east-northeast under the influence of increasing westerlies ahead of a deepening mid-latitude trough forecast to dig southeastward out of Canada and into the extreme northwestern Atlantic Ocean. The new official forecast track is very similar to the previous advisory track, and lies close to a blend of the tightly packed consensus track models. Humberto now appears to be well on its way to becoming a hurricane fairly soon based on the newly formed central dense overcast and mid-level eye feature. Although the large-scale shear is fairly large in the SHIPS intensity models, the shear directly over the center of Humberto is forecast to remain low for the next 48 hours or so, which should allow for steady strengthening. By 72 hours, the cyclone is forecast to be situated in the right-rear quadrant of a strong, anticyclonically curved jet maximum. The associated upper-level divergence is expected to induce strong pressure falls and strengthening despite the vertical shear increasing to more than 30 kt. By 96 hours and beyond, slightly cooler waters, much drier air, and very hostile shear conditions of more than 40 kt should cause steady weakening. The new NHC intensity forecast follows the trend of the previous advisory, but now shows Humberto reaching peak intensity in 72 hours, coincident with the warmest water temperatures of about 29C and greatest jetstream dynamical forcing. Large swells from Humberto will affect portions of the northwestern Bahamas and southeastern United States coast during the next few days. These swells are expected to produce dangerous surf conditions and life-threatening rip currents. See products issued by your local weather office for additional information. FORECAST POSITIONS AND MAX WINDS INIT 15/1500Z 28.9N 77.9W 55 KT 65 MPH 12H 16/0000Z 29.5N 77.7W 65 KT 75 MPH 24H 16/1200Z 30.0N 77.1W 70 KT 80 MPH 36H 17/0000Z 30.3N 75.9W 80 KT 90 MPH 48H 17/1200Z 30.7N 74.4W 85 KT 100 MPH 72H 18/1200Z 31.6N 69.6W 95 KT 110 MPH 96H 19/1200Z 34.5N 62.8W 85 KT 100 MPH 120H 20/1200Z 39.0N 57.0W 65 KT 75 MPH $$ Forecaster Stewart
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