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July 20, 2010 / Dave Gorham

Is Tropical Storm Bonnie on the Near Horizon?

Guest-blogger Chris Hebert, ImpactWeather’s lead hurricane forecaster, kindly posts for YWB today courtesy of the blog he produces for PennWell.

Last week I wrote about hurricane climatology and the fact that the tropics typically come alive right around the end of July.  I also mentioned that models were indicating increased thunderstorm activity across the Caribbean Sea and southwest Atlantic for this week, and that we may well be looking at possible tropical storm development by about now.  And as it turns out, we are seeing what quite possibly could be Tropical Storm Bonnie in its formative stages near the northeast Caribbean today.  Here’s a satellite shot showing what we’re identifying as Disturbance 22 and the location where we think that a low center could be forming.

One thing that’s apparent on the satellite image above is that thunderstorms are on the increase and there is some curvature or banding present.  That’s a sign of a developing circulation center.  Currently, wind shear across the disturbance is a bit on the high side, making its appearance on satellite even more impressive.  But that wind shear should be steadily diminishing over the next 48 hours, leaving a favorable environment for development.  With that in mind we’re now estimating that the chances of Disturbance 22 developing into the second tropical storm of the season to be 60%.  And there may be a good chance that if it does become a tropical storm that it could reach hurricane strength in 3-4 days.  But where will it go?

The graphic above represents all past July tropical storms and hurricanes which passed within 100 miles of the projected track of the disturbance.  There weren’t very many such storms, but climatology does suggest that Florida is the typical target of storms in this region.  Now let’s examine where current model guidance is projecting the disturbance/potential storm to track.

As one can see from the latest computer model plots above, there is quite good agreement among the better models in a track toward southeastern Florida.  Now, just because there is good model consensus doesn’t always mean that they’re right.  In this case, though, I think that the models have a fairly good handle on things.  The biggest uncertainty is just when the disturbance will develop.  And where it develops will ultimately play a large role in where it tracks.  If it develops earlier, then a track more to the right is more likely.  Later development may increase the risk to the Gulf of Mexico, perhaps as far west as Louisiana.  You can see our track in dark blue on the graphic above, taking the system inland near Miami and clipping the northeast Gulf on its way to a final landfall along the central Florida Panhandle on Sunday.

Anyone living or working anywhere from Louisiana to the Carolinas should be paying very close attention to this disturbance.  While I don’t think there is a high chance that it will be a large and powerful hurricane at landfall, there is most definitely a chance it could become a hurricane before it reaches Florida.  And even a small hurricane can produce considerable damage.

I’ll post an update to this morning’s TropicsWatch Daily Briefing on our YouTube channel this afternoon.


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