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| #982209 (Received by flhurricane at: 4:44 AM 14.Sep.2019) TCDAT4 Tropical Storm Humberto Discussion Number 7 NWS National Hurricane Center Miami FL AL092019 500 AM EDT Sat Sep 14 2019 Convection associated with Humberto has increased a little since the last advisory, as a new burst has occurred to the north of the center. Other convection continues in a large curved band in the eastern semicircle. Reports from an Air Force Reserve Hurricane Hunter aircraft near 0500 UTC indicated that the maximum sustained winds were near 35 kt, and that will be the initial intensity for this advisory. It should be noted that an upper-level trough is located just south of Humberto, and the storm may have some subtropical characteristics due to interaction with this trough. While the motion is still a bit erratic, Humberto now seems to be moving a little faster toward the northwest or 315/6 kt. During the next few days, a low- to mid-level ridge over the eastern United States and the western Atlantic is expected to slide southeastward, with a weakness in the ridge developing due to a mid- to upper-level trough over the northeastern U.S. This change in the steering pattern should cause the storm to slow down and turn northward off the east coast of Florida in 36 to 48 hours. Subsequently, the northeastern U.S. trough should dig southward, and this change should turn Humberto northeastward and then eastward away from the U.S. The track guidance has shifted a little more to the east during the first 72 h, and the new NHC track has been nudged eastward as well during this time. The new forecast track lies near the various consensus models. Southwesterly vertical shear and dry air entrainment caused by the upper-level trough to the south is forecast to diminish during the next 2-3 days while Humberto moves near or over the warm waters of the Gulf Stream. This should allow intensification, and Humberto is expected to become a hurricane in about 48 h. The intensity forecast becomes more uncertain between 72-120 h. Strong upper-level winds associated with the mid-latitude trough over the eastern United States should cause strong shear over Humberto. However, there is a chance that baroclinic forcing from the trough could compensate for the shear, and the GFS, ECMWF, UKMET, Canadian, and HWRF models all show the central pressure falling during this time. The intensity forecast will follow this guidance and show some additional strengthening through 96 h. Overall, the new intensity forecast is similar to, but slightly higher than, the previous forecast. Key Messages: 1. Humberto will likely bring tropical-storm-force winds and heavy rainfall to portions of the northwestern Bahamas today. Significant storm surge is not expected in the northwestern Bahamas from this system. Residents there should follow any advice given by local officials. 2. Since the forecast track has shifted farther to the east, the chance of heavy rainfall affecting the southeastern United States has diminished. FORECAST POSITIONS AND MAX WINDS INIT 14/0900Z 26.3N 76.0W 35 KT 40 MPH 12H 14/1800Z 26.9N 76.9W 40 KT 45 MPH 24H 15/0600Z 28.0N 77.7W 45 KT 50 MPH 36H 15/1800Z 29.0N 77.9W 55 KT 65 MPH 48H 16/0600Z 29.8N 77.4W 65 KT 75 MPH 72H 17/0600Z 30.8N 74.7W 75 KT 85 MPH 96H 18/0600Z 31.5N 71.0W 80 KT 90 MPH 120H 19/0600Z 33.0N 66.0W 75 KT 85 MPH $$ Forecaster Beven |
