Dr. William Gray's April 2005 Predictions

The cyclone phase analyses from the available models all suggest a shallow warm-core with the system, or more or less your typical secluded-type of structure. You don't see it all too often along the east coast of the U.S. -- you see it a lot more south of Greenland -- but on occasion, you can see what we've got out there right now. Nothing tropical or even subtropical about it, just something nice to look at.

Current as of this evening: http://moe.met.fsu.edu/cyclonephase/compare/05050818/M4.html; see http://moe.met.fsu.edu/cyclonephase/ for future runs. As an aside, the cyclone phase diagrams were developed initially based upon comments made by Jack Beven, who is a big followed of the hybrid storms (for what it's worth), about the thermal structure of tropical vs. extratropical cyclones.

SSTs in the region are <20 C (not favorable for tropical/subtropical development) and the system is definitely still frontal in nature; one good look at satellite confirms this; the South Atlantic system last week at least was somewhat separated from its old frontal structure before it was completely overtaken by an onslaught of cold air from the south. An upper-level low wrapped around the North Atlantic system yesterday, enhancing the upper level circulation; the fact that it has sat right along the boundary of the Gulf Stream & the colder waters north of it has enhanced the available surface energy for the system. The acquisition of the low-level warm core either came about as a natural progression of the storm into the seclusion phase (which isn't well understood yet) or out of convective warming near the core of the system. The upper-levels, however, are still cold-core, one of the first indicators that the system isn't nearly tropical.

Polar lows often times can have eye-like features associated with them, and do note that by definition, the wind at the center of a low pressure system should be near zero...so those two features alone do not give you a tropical cyclone.

Wind field: http://manati.orbit.nesdis.noaa.gov/dataimages21/cur_hires/zooms/WMBas86.png. Note the overall expanse of the circulation and the large swath over which the maximum winds cover. This is neither indicative of a tropical (relatively compact wind field, strongest winds confined to a very narrow band near the center & rapidly dropping off outward from there) or subtropical (similar to tropical but with a looser definition, namely slightly larger expanses) cyclone structure. Other adjacent images suggest frontal structures still associated with the system.

In a few words, pretty to look at but nothing compared to what we'll see in a month or two. As an aside, Atlantic SSTs are running 1 deg C (or greater) above normal east of Hispaniola, with SST anomalies of 3 deg C above normal just off of the coast of Africa. The 26 C isothem sits at 15 N at < 40 W and 20 N from 45 W on westward. The coolest locations are off of both shores of Florida, where we have seen a cooler-than-normal spring. These are the shallowest waters, however, and can warm up in a hurry from where they sit now. All of this portends what *may* be an early start to the deep Atlantic tropical season (though, admittedly, a slow start to the near-shore season).

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