Subtropical Storm Andrea–Analysis

Good morning everyone. I had hoped to have some analysis on Andrea sooner, but didn’t get around to writing something up. Anyway, Andrea was originally an extratropical system that gradually picked up some tropical characteristics early last week. As a result, it became more of a hybrid system, one that wasn’t quite tropical, but also wasn’t purely a mid-latitude system either. While the system had tropical storm force winds, it was also still a cold core system. Tropical storms and hurricanes are warm core systems. When we say warm core, or cold core, we are talking about the characteristic of the air near the center of lowest pressure.

Early Start To 2007 Atlantic Season

Traditionally, the Atlantic Hurricane Season runs from June 1st to November 30th, or coincides between the start of meteorological summer and the end of meteorological autumn. With Andrea becoming the first named storm of 2007, the Atlantic season unofficially got underway some three weeks or so ahead of schedule. Although this is rare, it does happen on occasion. For instance, back in April 2003, the first named storm of that season, Ana, developed in late April around Easter. As a matter of fact, when you look at the monthly storm totals courtesy of the Hurricaneville Information Center Database, you might actually be surprised. During the months of January through May, there have been 6 subtropical storms, 19 tropical storms, 5 hurricanes, and one major hurricane of Category Three Strength or higher on the Saffir-Simpson Scale since 1851. In light of the fact that last year was such a quiet season, and that the country is not yet at an adequate level of hurricane preparedness, Andrea served as a welcome wake-up call.

Storm Strength

Obviously, Andrea wasn’t your classic hurricane. At peak intensity, Andrea had winds of 45 mph, and a minimum barometric pressure of 29.62 inches of Hg, or 1003 millibars. The storm didn’t have much endurance either as it only lasted some two days as a named storm or depression. There were several reasons for this. First, the storm was in unfavorable waters. During the month of May, sea surface temperatures off of the Southeast coast are below 80 degrees Fahrenheit, which is necessary for tropical development. At the time Andrea was forming, water temperatures were reported to be about 77 degrees. Another reason was the slow, or even non-existent motion of the system. Storms that move slowly, drift, or become stationary have a tendency to bring up cooler waters from deep below the surface in a process called upwelling. The third, and final reason was the fact that there was plenty of dry air to the west of the storm thanks to high pressure over the Southeastern United States. As a matter of fact, the dry air was also responsible for fueling the drought and brush fires in Southeastern Georgia and Northern Florida recently. Dry air sinks, which prevents thunderstorms from developing.

Andrea Unable To Provide Much Needed Rain To Southeast

When Andrea formed, forecasters had hoped that it would bring much needed rain to the Southeast, which is facing its worst drought in several years. Portions of Southeast Georgia including Waycross are battling devastating brush fires as a result of the lack of rain in the area. Northern Florida communities such as Jacksonville are suffering as well. As a matter of fact, much of Florida is dry this Spring with Lake Okeechobee running several feet below normal, and spots in the lake are actually bone dry. The lake is a critical water source for milions of people in the Everglades region of South Florida. Although Andrea brought plenty of coastal flooding and beach erosion, it was unable to come ashore and move inland to provide drenching rains to places that desperately need it.

Harbinger Of Things To Come?

Could the formation of Allison mean that the Atlantic will be back in 2007? Perhaps. While the 2006 Atlantic Hurricane Season was below normal in terms of activity, the El Nino that developed, and was largely responsible for keeping storms to a minimum, has dissipated. Forecasters such as Dr. William Gray of Colorado State already have indicated that there will be at least 17 named storms, 9 hurricanes, and 5 major hurricanes in 2007. Those numbers are up a bit from projections made in December of 14 named storms, 7 hurricanes, and 3 major hurricanes. The Atlantic continues to be in the midst of a very active period. Since 1995, there have only been two years where activity was below normal: 1997 and 2006, which were both El Nino years.