31 October 2022

Season's 12th named storm forms on Halloween

Tropical Storm Lisa formed today in the central Caribbean, just south of Jamaica.  This has been a feature of interest for about six days already, but it failed to develop near the Lesser Antilles and the eastern Caribbean. Even today, it looks marginal on satellite, but aircraft data confirmed the organization and intensity necessary to upgrade it to a tropical storm.

Despite the extremely warm ocean water in the western Caribbean, Lisa continues to face some environmental challenges to intensification.  There's quite a bit of dry air to the west, and some of that is wrapping into the circulation now and will continue to linger.  The storm is also in fairly strong vertical wind shear as evident in the satellite animation above -- the low-level center is completely exposed and the thunderstorm activity is all displaced to the east and south.  

Over the next couple of days, the shear is expected to relax somewhat, and that in turn will reduce the amount of dry air that reaches the storm center.  This 3-day forecast from the American GFS model shows the mid-level humidity in the colored shading, and it illustrates the gradual moistening of the storm environment before it makes landfall.

The model guidance is fairly clustered on the track, but more scattered on the intensity.  For track, Lisa will continue to head west across the Caribbean, reaching Belize midday Wednesday.  For intensity, the large majority of models keep it as a tropical storm, but there's an outside chance that it could reach hurricane intensity prior to landfall.  The official forecast (as of 11am EDT) is on that high end and indicates a minimal Category 1 hurricane at landfall... if model trends continue to drop, the subsequent NHC forecasts will certainly reflect that.

Lisa is the season's 12th named storm... you have to go back to 2015 to find so few storms by the end of October, and in terms of Accumulated Cyclone Energy (ACE), the season is at about 73% of average for the date.

Elsewhere, the Atlantic is quiet and there's no sign of new development within the next week or so.

12 October 2022

Karl forms and threatens Mexico with heavy rain

First, a bit of catching up: I was on vacation last week and didn't write anything about Hurricane Julia which formed near Aruba, tracked west and developed into a hurricane as it made landfall in central Nicaragua, and then had a complicated evolution over Central America.

Like Bonnie back in early July, Julia made landfall in Nicaragua and traversed the country intact, maintaining its identity as a tropical storm in the East Pacific.  Julia made another landfall in El Salvador then dissipated over Guatemala, but a part of the circulation split off to the west and is an area of potential development (Invest 99E) in the East Pacific while another part split off to the north and became Tropical Storm Karl on Tuesday afternoon.

The map above shows an infrared satellite image from Wednesday morning, but I superimposed the tracks of Hurricane Julia, Tropical Storm Karl, and Invest 99E for reference to illustrate the interesting split that Julia's remnants experienced.

Julia was the season's 10th named storm and 5th hurricane, so Karl is the season's 11th named storm -- it is not expected to reach hurricane intensity as it drifts back south into the Veracruz area of Mexico over the next couple days.  The greatest threat is heavy rain resulting in flooding and mudslides.

The season's storm tally as of October 12 is at 11 named storms, 5 hurricanes, and 2 major hurricanes (Category 3+).  This table shows the average dates by which these milestones occur... you can see that by now, an average season would have 12 named storms, 5 hurricanes, and 2 major hurricanes, so 2022 is really close to those marks.

We can also look at the season's activity in terms of Accumulated Cyclone Energy, or ACE, which is a metric that doesn't depend on the number of storms, but on the overall intensity and duration of whatever storms there are.  By this metric and the same baseline as before (1991-2020), the season is only 79% of average for the date.

Elsewhere, the Atlantic basin is quiet with no activity in the foreseeable future.