D.C. Rain Linked to Intensity of Hurricane Season?
Have you noticed the lack of rain lately? Our rainfall deficit since July 1 is almost 5", and "abnormally dry" conditions are closing in on the region according to the U.S. Drought Monitor. At the same time (as our hurricane expert Greg Postel just explained), the hurricane season has been eerily quiet, with only 6 named storms in the Atlantic basin. So, does the dearth of rain have anything to do with the anemic hurricane season?
In many years, we receive significant rainfall from the remnants of tropical storms and hurricanes after they make landfall. So, intuitively, it would make sense if our wettest (driest) late summer and early fall periods coincided with active (inactive) hurricane seasons.
The logic behind this reasoning: the more hurricane activity, the greater the odds of a storm making landfall, and the greater chance our region would get some of the rain. Over the weekend, I decided to examine the data to see if this hypothesis had any legitimacy. The answer: kind of.
I plotted an index of hurricane activity known as ACE (Accumulated Cyclone Energy) against the rainfall at Reagan National during the months of July-October for the period 1950-2008. There was a correlation, but it was weak (r-squared of 0.17). However, what was most revealing to me was the rank of the wettest (driest) years compared to the rank of the most (least) active hurricane seasons.
Nine (ranks 1, 2, 3, 4, 6, 8, 9, 11, and 12) of the top-15 most active hurricane seasons coincided with the 15 wettest years at Reagan National in the 59 year period (and nine of the top-15 wettest years coincided with the top-15 most active hurricane seasons). Only 3 (ranks 7, 10, and 13) of the top-15 most active hurricane seasons coincided with the driest 15 years. And none of the 15-wettest years coincided with the 15-least active hurricane seasons.
These findings, therefore, make it no surprise that this year has been dry. 2009's ACE is just 40 -- which would make it the 14th least active since 1950 (of course it could still increase if more storms are named).
What this quick and dirty analysis implies to me is that a very active hurricane increases the likelihood of a wet late summer to early fall period in D.C. while an inactive hurricane season increases the chances of a dry period, as has been the case this year.
| September 24, 2009; 10:30 AM ET
Categories: Local Climate, Tropical Weather
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