Andrea slowly weakening

Subtropical Storm Andrea has weakened this morning, and currently poses little threat to land--other than some minor beach erosion along the Georgia and northern Florida coasts. Storm tides are running about one foot above normal in these areas, with 2-4 foot surf. Andrea's satellite presentation shows a classic example of a weak storm experiencing significant wind shear. Most of the heavy thunderstorm activity is displaced to the east side of the storm, pushed there by strong upper level winds from the northwest and west. Wind shear is about 20 knots, and is expected to remain this high for another day, then decrease by Saturday. The organization of the spiral bands of rainfall visible on the Jacksonville, FL long range radar is poor. The top winds found by the Hurricane Hunters this morning at their flight level of 1000 feet were 41 mph, as of 9:20am EDT. The central pressure had risen to 1003 mb, according to their 9:20am center fix, and Andrea may get downgraded to a tropical depression later today. The GFS model is calling for Andrea to dissipate by Saturday, and given the marginal Sea Surface Temperatures (24-25 C), significant dry air surrounding the system, and strong wind shear, NHC is also calling for dissipation. However, there is a good possibility that Andrea could hang on and eventually get swept out to sea, as the GFDL model is calling for. In this scenario, Andrea could intensify early next week and threaten Bermuda as a strong subtropical storm.


Figure 1. Forecast smoke levels at 11am EDT Thursday, May 10 from NOAA's air quality computer model. Note the ring of smoke encircling Jacksonville, due to the counterclockwise flow of air around Andrea. Image credit: NOAA.


Figure 2. Observed levels of fine particulate matter pollution (PM2.5) over Florida. Orange circles mark cities where the air is "Unhealthy for Sensitive Groups", and people with heart or lung disease, older adults, and children should reduce prolonged or heavy exertion in these areas. Image credit: EPA.

Andrea and the Florida/Georgia fires
The counter-clockwise circulation of air around Andrea's center of low pressure can be seen in the forecast movement of smoke from the fires burning in northern Florida and Southeastern Georgia (Figure 1). The Hurricane Hunters reported that dense smoke was obscuring visibility over the ocean waters near Jacksonville during their mission into Andrea this morning--the first time I've ever seen that observation during a hurricane hunter mission. This smoke is expected to form a ring encircling Jacksonville, and an air pollution alert for unhealthy levels of particulate matter pollution has been posted today for that city. Particulate matter pollution advisories have also been posted along a swath from Orlando to Miami. People with heart or lung disease, older adults, and children should reduce prolonged or heavy exertion in these areas. A map of current particulate matter pollution levels is posted in Figure 2. Wunderblogger aquak9 has a Floriga/Georgia fire blog for those interested in conversing about the fires.

Rainfall from Andrea has been less than 0.3 inches across the fires zones, which is not enough to douse them. Andrea is a very dry storm; peak rainfall rates are only about 0.25 inches per hour, in the storm's southeastern rainbands. These rainbands are not expected to hit the coast in the next two days. Maximum total rainfall observed by the Jacksonville radar has been less than 1.5 inches.

I'll have an update Friday morning, unless some significant change in Andrea occurs today. The 8am QuikSCAT pass missed Andrea; the next pass is at about 8pm. The next Hurricane Hunter mission is not until 8am Friday.

Jeff Masters