Updated 11:11 am on September 20th to reflect change 11 am advisory changes.
This weekend marks the “peak” of the Atlantic hurricane season, and if you look at the latest National Hurricane Center tropical weather outlook, nature is right on schedule. At the time of writing Saturday morning, I count six areas systems including two Tropical Storms (Paulette and Rene), Tropical Depression Nineteen, and three areas of interest. Tropical Depression Nineteen is the one that I want to focus on because it is a sneaky little threat for Florida and the Gulf Coast states.
American GFS model forecast for what could be Tropical Storm Marco near the Louisiana coast by … [+]
Our meteorological models have been sniffing out the possibility in recent days that Tropical Depression Nineteen could be a problem for Florida and the Gulf Coast states. Brian McNoldy, a hurricane expert at the University of Miami, writes an excellent blog that I highly recommend for everyone. On September 10th he wrote, “Aside from Tropical Storms Paulette and Rene in the central Atlantic, there are two weak waves in the western Atlantic — one approaching the Bahamas and heading west, and another west of the Florida peninsula and heading west.”
While he wasn’t bullish on them becoming tropical cyclones, he also noted, “but it’s not out of the question either.” By September 11th, some of our regional models had become extremely bullish on the system approaching Florida. IBM/The Weather Company tropical weather expert Michael Ventrice tweeted, “12Z HWRF is trying to spin up Invest #96L into a strong Tropical Storm/low grade Hurricane as it pushes over the warm Northeastern Gulf of Mexico waters early Monday morning.” The American GFS and European model now have similar trends for the storm to likely become “Sally.”
Simulated satellite image of what could be Tropical Storm Marco by Sunday morning.
What’s the current status of the storm? To answer that question, I consult the National Hurricane Center. As of 8 am on the morning of September 12th, the storm was exiting the Florida panhandle and had sustained winds of 35 mph, which is just below the 39 mph threshold designated for tropical storms. The storm was moving westward at 9 mph but will eventually take more of a northwestward track with a possible landfall somewhere near New Orleans, Louisiana. (Note: At the 11 am update, the National Hurricane Center now expects the storm to be a hurricane just before landfall)
11 am advisory on what is expected to become Tropical Storm and Hurricane Sally
The key messages of the National Hurricane Center are summarized:
- Isolated to scattered flash flooding across portions of west-central and southern Florida and prolonged minor river flooding across Central Florida through Sunday.
- Scattered flash flooding is also possible across portions of the central Gulf Coast Sunday through Tuesday morning.
- Tropical storm conditions possible by Sunday evening in the Florida Panhandle (a Tropical Storm Watch has already been issued.)
- Strong tropical storm or even a minimal hurricane by the beginning of the week with impacts (storm surge, rainfall, winds, tornadoes) from the Florida Panhandle to southeastern Louisiana.
The sea surface temperatures and wind shear in the Gulf of Mexico region
There is plenty of warm water in the Gulf of Mexico, but forecast models anticipate that some wind shear could potentially hinder storm development though the wind shear analysis from the CIMSS tropical webpage (above) does not suggest that shear is too unfavorable ahead of the storm right now. The ultimate intensity of the storm will depend on the delicate dance between “ample fuel supply (warm water)” and wind shear. If Sally does form, we will be down to three names left on the 2020 season list with much it still ahead of us. Greek alphabet anyone?
National Hurricane Center 5-day outlook as of Saturday morning (September 12th).
