Could Bill redevelop? Not likely…but not impossible…

Good evening.

Much of the discussion has been on Tropical Storm Bill (or at least its remnants). However, some model runs have suggested it may actually redevelop after the low emerges in the Atlantic late this weekend or early next week. Interestingly, they actually maintain the low as a warm-core feature in the northern Atlantic, south of Nova Scotia and southeast of New England. The 12Z ECMWF is one model run that redevelops Bill offshore. Is it possible? Yes, but not likely. Most other models do not do such a thing.


ECMWF model run issued at 1200 UTC (8:00 am EDT) June 18, 2015. Notice the new low, which at best is neutral temperature wise (and possibly warm core) south of Nova Scotia.

The case for redevelopment

Sea surface temperatures, although marginal, are running well above average for mid-June in the northwestern Atlantic Ocean, especially near the Gulf Stream. The higher temperatures (about 3 to 5°C, or 5 to 9°F, above normal) could be what the low needs to redevelop and regain (or hold onto) tropical characteristics. In addition, Tropical Depression Bill has retained a remarkably good structure so far for being inland for over 36 hours, and is clearly still tropical as it tracks across the Missouri Ozarks. The heat to the south, along with more moist conditions along the track, may help it maintain strength.


Sea surface temperature anomalies. Notice the oranges and reds off the Northeast coast.

The case against redevelopment

First of all, the WPC currently predicts that Bill may lose tropical characteristics as it races eastward this weekend. Climatology also strongly objects to such a redevelopment, and it will likely only occur if Bill emerges in the Atlantic south of about 39°N latitude (roughly the latitude of Cape May, New Jersey) as water temperatures drop off rapidly north of there. Most models track the remnants across the southern Great Lakes and southern New England (or just south of), where water temperatures are much too cool and dry air would be a more significant factor. Finally, wind shear would be much greater to the north due to the presence of the frontal boundary and jet stream. By definition, a tropical cyclone is non-frontal and cannot be associated with a frontal zone.


I would put the potential for redevelopment at approximately 20%. It has some model support, but not a great deal, and the conditions aren’t that ripe for such. If redevelopment occurs, tropical storm conditions are likely near the center of the storm, which would be mostly over water. Even if it is extratropical (like a Nor’easter) and strengthens, winds may be strong for some areas.

Finally, would it still be named Bill? The answer is YES, as long as an identifiable low pressure area at the surface can be tracked, which most models suggest will happen. That is not unlike the situation in 2004 with Hurricane Ivan detaching and redeveloping in the eastern Gulf of Mexico, with the upper-level remnants continuing into Atlantic Canada.

We will all keep you updated over the weekend and monitor the conditions for you. I am on Twitter at @EternalWeather1.

Forecaster Craig Ceecee

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