Invest 95L May Become Subtropical Storm Chris

The tropics are starting to heat up again. The feature of intertest I want to focus on today is Invest 95L.

Invest 95L:

Invest 95L is a low that has spun up off a frontal boundary. For those who have been following the tropics earlier this season, you probably know what this means: another subtropical cyclone. Invest 95L is located just NE of Bermuda and it is easier to see its location via the NHC Tropical Weather Outlook map:


95L is the orange circle on the above map, which the NHC is giving a 30% chance of becoming a subtropical or tropical cyclone over the next 48 hours as of 8am EDT today.

Satellite imagery shows that 95L already has a closed surface circulation and has recently began firing deeper convection over the center of the storm:

Visible Satellite Imagery of 95L

Infrared satellite imagery makes it easier to see how deep the convection is:

IR satellite image of 95L

The fact that 95L is firing deeper convection is a sign that the system is starting to gain some, or most of its energy from the warm waters of the Atlantic Ocean rather than the baroclinic energy of the frontal boundary. Sea surface temperatures are currently about 24C under the center of the storm, which is usually not warm enough to support a fully tropical cyclone, but plenty warm enough to support a subtropical cyclone.

These observations are supported by today’s 06Z GFS phase analysis, which shows Invest 95L has recently transitioned into a warm core (subtropical/tropical) cyclone:

06Z GFS Phase diagrams for 95L

The top right quadrant represents a asymmetric warm core cyclone, which usually refers to a subtropical cyclone. The bottom right quadrant represents a symmetric warm core cyclone, which usually refers to a fully tropical cyclone. The ‘A’ is where the low originated, the ‘C’ is where the low is currently located, the ‘Z’ is where the low will be when the forecast cycle ends.

I would normally be skeptical of a system this far north at this time in the year becoming a fully tropical cyclone as the GFS is suggesting. However, 95L is situated right over the warm waters of the Gulfstream. In fact, SST analysis from NOAA shows there are pockets of 26C waters in the path of 95L. 26C waters are usually referred to as the benchmark temperature needed for a system to become a tropical cyclone.

Taking all this into account, I would give Invest 95L about a 50% chance of becoming at least a subtropical cyclone. If this were to occur, it probably would happen sometime tonight or tomorrow morning.

Regardless of whether or not 95L can become subtropical storm Chris, it should have no impact on land. 95L will progress NE today and then turn more eastward and out to sea in a couple of days where it will become post-tropical.

It is quite rare to get to the third named storm of the season by mid-June. However even if this does happen, I still do not think this is a precursor of a very active season as all three of these possible storms would have been subtropical in origin rather than tropical. If we had three storms that were all tropical in origin by mid-June this would probably suggest that the Atlantic is much more conducive for tropical cyclone formation than climatologically expected. However, this is not the case and I still expect an average number of named storms this year (12).

Elsewhere in the Atlantic there is the possibility of tropical cyclone formation in the NW Caribbean Sea or Gulf of Mexico later this week, and I will have an update on this later.



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