Thursday, June 6, 2013

Andrea ... a problematic forecast

Forecasting the strength, track and location of heaviest precipitation with Tropical Storm Andrea isn't easy.

The ramifications are huge for the Charlotte region.  Someone along Andrea's track stands to get 3 or 4 inches of rain, and if that falls in the immediate Charlotte area, we'll be looking at some real flooding problems from late tonight until midday Friday.

One thing to watch is the transformation of Andrea from a tropical to an extratropical system.

As a tropical storm, Andrea's heaviest rain is close to the center. In tropical weather systems, the worst conditions typically are in the eastern quadrant.

But as these storms lose their tropical characteristics, the rain shield tends to expand -- especially on the west side of the storm's center.

The question is when Andrea will become extratropical.  If that happens fairly early, before the storm's center moves into South Carolina, the heavy rain bands will spread into the Charlotte region. In fact, the foothills and mountains will get in on the action.

(Incidentally, separate low pressure systems could bring heavy rain to the mountains Friday night, long after Andrea has zoomed up the East Coast.)

We'll keep an eye on this during the evening and early Friday.