26 October 2020

Hurricane Zeta and déjà vu for Louisiana

On Monday afternoon, Zeta was upgraded to the season's 11th hurricane.  Looking back to 1851 when official records begin, only two previous seasons had 11+ hurricanes by this date: 2005 (13) and 1950 (11), so this is a truly remarkable level of activity. 

But, as if having 27 named storms and 11 hurricanes this season were not enough, Zeta looks like it will make landfall in roughly the same place where Tropical Storm Cristobal did in early June, Hurricane Laura in late August, Tropical Storm Marco in late August, Hurricane Sally in mid September, and Hurricane Delta in early October. It's only 340 miles between Sally's landfall point in eastern Alabama and Laura's landfall point in western Louisiana.

Zeta is forecast to clip the northern Yucatan peninsula on Monday night into Tuesday morning as a hurricane, then enter the Gulf of Mexico. While it should maintain hurricane intensity through its U.S. landfall on Wednesday, model guidance is consistently showing it weakening a bit as it approaches land, so it *could* be a tropical storm by that time. Regardless, heavy rain, strong wind, and storm surge will be hazards across a wide area. Keep in mind that a hurricane's impacts are far larger than a track line or the "cone of uncertainty".

Regarding track guidance, two of the global ensembles are packed pretty tightly now, with solutions ranging from western LA to the western tip of the FL panhandle, clustered most tightly around central-eastern LA.

The official hurricane season ends in 35 days, but nature does not have to stick to that artificial bound, so there's plenty of time for more storms this season. The next couple of names on the list are Eta and Theta. There's a slight hint among long-range models of another development in the western Caribbean in 10-14 days, but that is too far out to be reliable... think of it as the next potential time and region of favorable conditions.

25 October 2020

Zeta becomes 27th named storm, threatens northern Gulf coast

After a seemingly-endless wait, the disturbance in the western Caribbean was upgraded to Tropical Depression 28 on Saturday night, and then to Tropical Storm Zeta on Sunday morning.  This is the season's 27th named storm, and ties the record 2005 season, at least by that metric.

Zeta is expected to continue to organize and intensify, possibly hitting hurricane status by the time it reaches the northern Yucatan peninsula on Monday night.  Then, the environment is forecast to become increasingly hostile and Zeta should begin to deteriorate as it nears the U.S. coast.  However, that doesn't eliminate impacts from it, so stay tuned as we get closer to the middle of the week (landfall should be some time on Wednesday).

As if stuck in a rut, Zeta is also forecast to make landfall along the northern Gulf coast, just as Cristobal, Fay, Laura, Marco, Sally, Beta, and Delta did before it this season!

Rainfall, as usual, is a concern with this storm.  As of Sunday morning, the only part of the U.S. that will be impacted by it in the near future is extreme south Florida, where flood watches are in effect through Monday. But the Yucatan and western Cuba will also see heavy rain, and eventually, the north-central Gulf coast region will in a few days.

Catching up on the ACE (Accumulated Cyclone Energy) metric, 2020 is at about 145% of average for the date, but we can see where it lies in relation to historical mega-seasons. The top 5 through October 25th are 1933, 1926, 2004, 2017, and 1893. 2005 and 1995 just fall short of that list at 6th and 7th places. 

Elsewhere across the basin, things look quiet in the foreseeable future. But if and when the time comes, the next couple of names on the list are Eta and Theta.

23 October 2020

As Epsilon passes by Bermuda, Zeta could form in western Caribbean

Hurricane Epsilon is now a Category 1 hurricane with peak winds of 85 mph... it's centered about 200 miles east-northeast of Bermuda.  It should remain a strong tropical cyclone through the weekend, but will gradually transition to an extratropical cyclone as it passes east of Newfoundland on Sunday. Then, it could actually be a pretty powerful storm for the British Isles by the middle of next week.

The area of disturbed weather in the western Caribbean is now labeled Invest 95L.  Although still not a tropical depression, its organization has improved drastically in the past day, and NHC is giving it a 60% probability of formation.  It's presently centered near the Cayman Islands, but is broad and messy.  

Any activity in the western Caribbean in October is cause for concern; some very notorious hurricanes have explosively developed there.  In this map of ocean heat content, high values over the entire western Caribbean mean that there is a nearly endless supply of very warm water at its disposal.  If this develops, it would be Tropical Depression 28 and then Tropical Storm Zeta. You may recall that the record 2005 season finally ended with Zeta, which formed on December 30th.

Model guidance is generally not aggressive with it (yet). We also need to interpret the guidance with caution, because models are not great with these broad and disorganized low pressure systems.  The overall consensus is for it to track toward the northwest, bringing it into the Gulf of Mexico early next week, perhaps as a tropical depression or tropical storm.  

But there are some notable outliers in both the global model ensembles and in regional hurricane models -- those outliers bring it north over Cuba and into south Florida or the western Bahamas on Monday-Tuesday. Those also happen to be the quicker and stronger solutions (this particular HMON run shown below ("HMNI") has a Category 1-2 hurricane just east of south Florida on Tuesday morning, for example). Given that this outcome would bring at least tropical storm conditions to urban southeast Florida starting Monday afternoon, it's worth keeping a very close eye on it.

With such a track spread, it's basically impossible to come up with a meaningful rainfall forecast. But Jamaica, Cuba, the Yucatan peninsula, the western Bahamas, and south Florida could easily see multiple days of heavy rain from today through Monday. Check https://www.nhc.noaa.gov/ for the latest forecasts.