19 September 2019

Humberto zips past Bermuda, Imelda drenching Texas, Jerry upgraded to hurricane

The tropical Atlantic continues to be buzzing with activity, which isn't surprising considering it's mid-September. We now have two hurricanes and a tropical depression.  Three other tropical waves have a shot at becoming tropical cyclones in the coming days as well.

Humberto made its closest approach to Bermuda on Wednesday night, and brought a peak wind gust of 116 mph to the island, knocking out power and momentarily knocking out the radar.  The final radar image before a 4-hour-long outage is shown below --  Bermuda was right in the southern eyewall of Category 3 Hurricane Humberto. It has since been downgraded to a Category 2 hurricane and is racing off toward the open northern Atlantic at 24 mph. It will become a large and strong extratropical cyclone by tomorrow.

Tropical Depression Imelda is still sitting over southeast Texas, and dumping FEET of rain in the same places that Harvey flooded in 2017.
Enhanced water vapor satellite image showing a large shield of cold cloud tops sitting over southeast Texas... very dry air is just to the west. (NASA)
Incredible rainrates of 4-6 inches per hour have set up and remained nearly stationary, resulting in rain being measured in feet rather than inches, and peak radar estimates are now over five feet. The loop below is a storm-total rainfall accumulation, where the scale updates to accommodate the maximum values.  By the end of the loop, the scale tops out at about 65 inches.

This once again serves as a reminder that it does not take a strong hurricane to cause tremendous destruction and impacts.  We saw this with Allison (2001), Harvey (2017), and Florence (2018) to name a few. Water is by far the #1 killer when it comes to hurricanes and tropical storms. Tropical cyclones and their remnants are still very wet, and when they become stationary, they're unbelievably wet. The hurricane rating scale (Saffir-Simpson Scale) is ONLY based on the storm's peak sustained wind speed... it says nothing about size of the wind field, rainfall, storm surge, or tornadoes. There's more to the story than the category!

Moving on to the newly-upgraded Jerry... it is now the season's 4th hurricane and is still headed toward the northern Leeward Islands.  Jerry should pass north of the Leewards on Friday, but could bring tropical storm force winds beginning Friday morning.  As of 11am EDT on Thursday, it has peak sustained winds of 75 mph and it's moving toward the west-northwest at 16 mph.

Model guidance is in quite good agreement on it recurving to the north prior to reaching the Bahamas later this weekend, but it is not a closed case. The skillful European model ensemble still has 10-15% of its members indicating that Jerry could remain to the south and track along/near the Greater Antilles. Assuming the most likely scenario, the only encounter with land it will have beyond the Leeward Islands is possibly Bermuda early next week -- about six days after Humberto's visit.
Of the three areas of possible formation shown on the map at the top of the post, the only one strongly supported by models is the easternmost.  A potent tropical wave inland over Africa is expected to come off the continent on Saturday and quickly get its act together.  The next name on the list is Karen.

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