16 September 2020

Sally makes landfall, Teddy upgraded to hurricane, Vicky weakens

For a few hours on Wednesday morning, the Atlantic basin was buzzing with three Category 2 hurricanes (Paulette, Sally, Teddy) and one tropical storm (Vicky).  Since my previous post on Monday afternoon, Sally weakened a bit on Tuesday but then intensified to a Category 2 hurricane as it made landfall on Gulf Shores, AL in the early morning hours on Wednesday. This is the *8th* named storm to make landfall on the mainland United States this season already... a new record.

The storm's slow forward motion continued through landfall (literally moving slower than a walking pace), creating tremendous flooding in parts of Alabama and the Florida peninsula.  I have long radar loops available at http://bmcnoldy.rsmas.miami.edu/tropics/radar/. Sally will continue to produce heavy rain along its track for the next several days, so the inland portion of its journey is just beginning.

Sally also generated something we tend to gloss over when it comes to hurricane impacts: the "anti-surge".  Storm surge is when strong onshore winds essentially and relentlessly bulldoze water onto land, often resulting in very destructive flooding.  But what about when the offshore part of the eyewall passes over a body of water? Well, Sally's western eyewall did just that: it passed over Mobile Bay and pushed a LOT of water out of the bay. At this tide gauge near Mobile, the water level fell 8 FEET as Sally made landfall, and then the water was eventually allowed to rapidly flow back into the bay. Of course, areas that experienced the eastern eyewall got the opposite effect.

Paulette was a hurricane up until midday Wednesday when it was officially transitioned from a tropical cyclone to an extratropical cyclone, at which point, NHC ceases advisories (though it's still a powerful low pressure system with hurricane-force winds!).

Vicky has remained a low-to-mid grade tropical storm, but is now weakening in the face of increasing wind shear (generated by Hurricane Teddy's outflow), and is expected to dissipate by the weekend.

Teddy has rapidly intensified to a Category 2 hurricane and is forecast to strengthen even more this week.  It's presently located about 750 miles east of the Windward Islands, 1350 miles southeast of Bermuda, and is moving toward the northwest at 12 mph. Models are in excellent agreement on a track toward the northwest, which unfortunately brings it to Bermuda on Monday -- they just got a direct hit from Category 2 Hurricane Paulette this past Monday!  Bermuda is the tiny cyan speck in the upper left corner of the satellite image below (can you find it?).

Then there are a couple areas of interest to monitor in the coming days. One is an easterly wave just south of Cabo Verde (Invest 98L). It's worth watching, but as of now, it faces a grim future according to long-range models.  While it's fairly likely to become at least a tropical depression in the coming days, the outlook as we head into early next head appears to include a more hostile environment for it. It's marginal though, with a few models showing continued development -- not an urgent threat to anyone.

The other is a disturbance in the western Gulf of Mexico (Invest 90L). It is in an area of virtually no steering flow, so it should just sit in place and gradually get organized.  What does the future hold for it? No model has a useful or consistent forecast, so for now, we wait and see what it does.

Only one name remains in the regular list: Wilfred.  After that, we start using names from the Greek alphabet: Alpha, Beta, Gamma, Delta, etc.  You may recall that the hyperactive 2005 season went into the Greek alphabet too, but not until October 22.  In terms of ACE (Accumulated Cyclone Energy), this recent burst of action has taken the season from near-normal a few days ago to about 125% of normal for this date.

As mentioned before, while the 2020 season is blasting its way through names, it's far from competing with previous hyperactive seasons in terms of ACE. The top five historical seasons as measured by ACE through September 16 are: 1933, 1995, 2004, 1950, and 2005.

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