Kirk forms, watching western Caribbean (again)

Since my previous post on Friday morning, Hurricane Isaac has transitioned to an extratropical cyclone north of the Azores, Invest 98L did become Tropical Storm Joyce but that is already on its way out, the easterly wave near Cabo Verde became Tropical Storm Kirk today, and there's another strong easterly wave trailing behind Kirk that has a high probability of formation (Invest 91L). We are still cautiously watching a broad disturbance in the southwestern Caribbean for signs of development.

Overview image showing the five areas of interest, overlaid on the sea surface temperature.  Isaac and Joyce are essentially done, Kirk just formed, and there are two other areas of potential development in the coming week.  Plot from Tomer Burg.

Let's start with Kirk.  This was Invest 98L on Friday, then was upgraded to Tropical Depression 13 on Sunday.  It was just upgraded again to Tropical Storm Kirk on Monday morning, making it the 11th named storm of the season.

Kirk is going to be moving into a very favorable environment for intensification, and is forecast to become the season's 3rd major hurricane in just a couple of days.  Thankfully, models are in excellent agreement on it turning north and staying way out over the open ocean.

The wave behind Kirk, tagged as Invest 91L, is currently centered just south of Cabo Verde and NHC is giving that a 90% probability of formation within a week -- models show this also becoming a strong storm in a few days and also likely to turn to the north, though perhaps waiting a bit longer to make that turn.  There is enough spread in the model ensembles that the Windward Islands may need to keep a close eye on this in 10-11 days, for what that's worth.  It's way too far out to worry about any details.  The next name on the list is Leslie.

ECMWF model ensemble spanning 2-10 days into the future.  Small red numbers mark the central pressures of trackable low pressure systems in the ensemble.

Last, let's shift west and look at the disturbance brewing in the western Caribbean.  NHC is giving this a 40% chance of development within a week, and the models have backed off a bit on intensification in the Gulf over the past 1-2 days.  These maps below show the tracks from the GFS (left) and ECMWF (right) ensembles through next Monday.  While there are plenty of weak and dissipating members, there are a few that merit continued attention.  *IF* it develops, a track toward Florida next Sunday-Monday is not out of the question among the stronger members.  Assuming Invest 91L takes the name Leslie in the coming days, this (if ever named) would be Milton.

In terms of overall Accumulated Cyclone Energy, the season is at about 83% of average for the date, but that will increase notably once Kirk is a major hurricane later this week.  The last time we had such an inactive June-September period was 2016.  That's especially remarkable considering how explosively this season began.

 

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