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| #982400 (Received by flhurricane at: 4:53 PM 15.Sep.2019) TCDAT4 Tropical Storm Humberto Discussion Number 13 NWS National Hurricane Center Miami FL AL092019 500 PM EDT Sun Sep 15 2019 Humberto's convective structure continues to improve in satellite imagery and reflectivity data from the Melbourne NOAA Doppler weather radar, including intermittent appearances of a closed eye. An Air Force Reserve reconnaissance aircraft investigating Humberto this afternoon found SFMR winds of 58-59 kt in the northeastern quadrant outside of the heaviest rain areas, and that the pressure had fallen 4 mb during the past 2 hours, now down to 989 mb. Based on these data, the intensity has been increased to 60 kt. The initial motion estimate is now 360/05 kt. There are no significant changes to the previous forecast track or reasoning. Humberto is likely located on or near an east-west oriented ridge axis, and a sharp turn toward the northeast is likely during the next 6-12 hours. The latest NHC model guidance remains highly convergent on the previous forecast track and continues to show the cyclone gradually being accelerated toward the northeast and east-northeast during the 24-120 hour period. The large deep-layer trough and associated cold front that will be digging southward out of eastern Canada and the northeastern United States is forecast by the ECMWF model to develop a cutoff low over the northwestern Atlantic that results in some binary interaction with Humberto on day 5. However, this is a new development and is considered to be an outlier scenario at this time. The new forecast track is similar to the previous advisory and lies close to the TVCN and HCCA consensus track models. Likewise, there is no significant change to previous intensity forecast. All of the available model guidance continues to support steady strengthening for the 3 days. In 48-72 hours, Humberto is forecast to be moving into the right-rear quadrant of a strong, anticyclonically curved 300-200 mb jet maximum. The associated strong baroclinic/dynamical forcing is expected to produce strong pressure falls and strengthening despite the hostile vertical wind shear conditions of at least 30 kt. On days 4 and 5, the combination of slightly cooler waters, drier and more stable air, and much stronger vertical shear of 40-50 kt should cause steady weakening despite the favorable jetstream dynamics. The previous NHC intensity forecast remains unchanged, and continues to show Humberto reaching its peak intensity in 72 hours, coincident with the warmest sea-surface temperatures and strongest 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 15/2100Z 29.3N 78.0W 60 KT 70 MPH 12H 16/0600Z 29.8N 77.6W 65 KT 75 MPH 24H 16/1800Z 30.1N 76.7W 70 KT 80 MPH 36H 17/0600Z 30.4N 75.4W 80 KT 90 MPH 48H 17/1800Z 30.7N 73.6W 85 KT 100 MPH 72H 18/1800Z 31.7N 68.9W 95 KT 110 MPH 96H 19/1800Z 35.0N 62.0W 85 KT 100 MPH 120H 20/1800Z 39.6N 56.1W 60 KT 70 MPH $$ Forecaster Stewart |
