TS Humberto Likely to Form- Could Bring Flooding Rains to SE United States

Potential Tropical Cyclone 9 is likely to form into Tropical Storm Humberto near the Bahamas and track towards the Florida coast. As of 0800AM EDT on Fri Sep 13, the National Hurricane Center forecasts an 80% chance that this low pressure system, which is now centered near the Bahamas, will develop into a tropical storm within 48 hours and a 90% chance that it will develop within the next five days. The disturbed area is now named "Potential Tropical Cyclone 9", but will be named Humberto if it becomes a tropical storm.

Five-Day Graphical Tropical Weather Outlook from the National Hurricane Center. Potential Tropical Cyclone 9 shown with a red X.

The best track forecast from the National Hurricane Center depicts a tropical storm approaching Florida's east coast, and then tracking from south to north very close to the coastline....a track quite similar to Hurricane Dorian's last week. However, until this system forms a center of circulation, we should expect storm track and intensity forecasts to change considerably.

The biggest concern with this system is the forecast stall near the Florida/ Georgia/ South Carolina coastline from Monday through Tuesday morning. If this forecast verifies, it could mean prolonged flooding rain for portions of the Southeast U.S. next week.

National Hurricane Center best track forecast for Potential Tropical Cyclone 9, as of Fri Sep 13 at 0800AM EDT

Most of the GFS (American) model tracks have shifted east over the past 24 hours. Yesterday, most ensemble members forecast Humberto to form and track into the Gulf of Mexico, but today most tracks forecast Humberto to form and track into the Florida Peninsula.

After tracking back out to sea before reaching Georgia, the GFS best track stalls the system in the Atlantic and forecasts the system to stall and then retrograde back towards the U.S. coastline close to North Carolina. Several models over the past two days have agreed with this idea...supporting a big picture of building high pressure over the Atlantic pushing potential Humberto back towards land after tracking into the Atlantic.

GFS ensemble models for Potential Tropical Cyclone 9- image from Tropical Tidbits

We should not focus on the details or exact track of such forecasts at this point, but keep in mind the big picture....it is possible that a tropical storm could form, potentially strengthen into a hurricane and impact the southeast U.S. The idea that this storm could possibly track out to sea and then be pushed closer to the coast again means that people north of the Carolinas should pay attention to this storm, as there is a possibility it could impact areas from the Chesapeake Bay to New England.

Global and hurricane model forecast runs for Potential Tropical Cyclone 9

Image: Tropical Tidbits

Most of the global and hurricane models depict this disturbed area to track to the northwest but remain offshore, then curve to the northeast and track off the Atlantic seaboard. Many of these models predict future conditions out to 120 hours, so they do not yet forecast what could happen past next Wednesday.

Marine Weather and Climate, Flood Information Systems and the U-Surge Project have initiated the first Hazard Area Likeliness (HAL) map for potential wind and flood hazards associated with this storm.

This map depicts that the biggest threat right now appears to be flooding from heavy rainfall. The HAL index forecasts the possibility of moderate damage from rainfall exceeding 8 inches from Mayport (near Jacksonville Beach, Florida) through Wrightsville Beach, NC. 

The possibility of moderate wind damage for the Mayport/ Jacksonville Beach area has also been added to this map.

Expect these forecasts to change considerably in the next 24-48 hours until a center of circulation forms and we have a named storm. All interests along the eastern seaboard of the U.S. should monitor the progress of this storm.