Tropical Storm Humberto Continues To Strengthen

At 5:00 PM Sunday AST, the National Hurricane Center continues to issue advisories on Tropical Storm Humberto, 335 kilometers north-northwest of Great Abaco Island.

The center of Tropical Storm Humberto was located by reconnaissance aircraft and NOAA Doppler radars near latitude 29.3 North, longitude 78.0 West. Humberto is moving toward the north near 9 KM/H, and this motion is expected to continue through tonight. A sharp turn to the northeast is forecast to occur Monday morning or afternoon, followed by a motion toward the northeast and east-northeast on Tuesday and Wednesday. On the forecast track, the center of Humberto will continue to move away from the Bahamas and remain well offshore of the southeastern coast of the United States through Wednesday.

Data from an Air Force Reserve reconnaissance aircraft indicate that maximum sustained winds have increased to near 110 KM/J with higher gusts. Further strengthening is expected during the next few days, and Humberto is expected to become a hurricane later tonight.

Tropical-storm-force winds extend outward up to 240 kilometers from the center. The minimum central pressure based on aircraft data is estimated to be 989 millibars.

Forecast Cone for Tropical Storm Humberto as of 5:00 PM Sunday 15th September 2019. Credit: National Hurricane Center

Watches & Warnings

Watches and Warnings in effect for Tropical Storm Humberto as of 5:00 PM Sunday 15th September 2019. Credit: National Hurricane Center
Watches and Warnings in effect for Tropical Storm Humberto as of 5:00 PM Sunday 15th September 2019. Credit: National Hurricane Center

There are no coastal watches and warnings in effect.

Hazards Affecting Land

Rainfall: Outer rain bands associated with Humberto are expected to produce additional rainfall of 1 to 2 inches in the central and northern Bahamas, with isolated storm total amounts of 6 inches. Humberto may bring periods of heavy rain to Bermuda beginning late Wednesday. Street and flash flooding are possible.

Seas: Swells generated by Humberto will affect the northwestern Bahamas, and the southeastern coast of the United States from east-central Florida to North Carolina during the next few days. These swells could cause life-threatening surf and rip current conditions.

This tropical storm is of no threat to the Lesser Antilles, including Trinidad and Tobago.

Tropical Storm Humberto Discussion

Tropical Storm Humberto churning north of the Northwestern Bahamas. Credit: Weathernerds

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 the 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 the 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.

Discussion by National Hurricane Center’s Forecaster Stewart

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