Hurricanes,Tropical Storms and the Gulf Oil Spill

I have been getting many e-mails and questions about the oil spill impacts on hurricanes and tropical systems in the Gulf of Mexico. I thought I’d get you the answers from one of my former professors at The Ohio State University and an expert on the topic. Dr. Jay Hobgood was one of my favorite professors in school and he’s what I would call a tropical meteorology specialist. I took several classes with him including a graduate level seminar class on Tropical Meteorology. I still remember my teaching topic was concentric eyewall theories by Hugh Willoughby. Well enough with my school days and more about the topic from Dr. Hobgood.

Brad

The following is an e-mail Dr. Hobgood sent out on our Climasp e-mail discussion group at The Ohio state University.

Associate Professor, Department of Geography, The Ohio State University
Director, Atmospheric Sciences Program, The Ohio State University

I have been getting questions like this a lot, especially as we approach the official start of the Atlantic Hurricane Season on June 1. There were also a fair number of informal conversations about this topic at the AMS Conference on Hurricanes and Tropical Meteorology last week in Tucson. So, I’ll give you my take below and I’m going to restrict my comments to the hurricane and weather questions and so please don’t misinterpret them as applying to the ecological effects of the spill.
I think the spill is likely to have only a minimal impact on the climate and weather including hurricanes that might pass through the region. First the area currently containing oil is relatively small in comparison to the area of the entire Gulf of Mexico. A very quick and rough calculation I did based on a NOAA map indicates that the spill encompasses an area of about 36000 square kilometers (14000 square miles). By comparison, the area of the Gulf of Mexico is approximately 1,600,000 square kilometers (615,000 square miles). So, the spill is currently affecting roughly two percent of the area of the Gulf of Mexico. The energy fluxes, evaporation and other transfers over the other 98% of the Gulf are currently unaffected by the spill.
The spill might have a greater impact on the evaporation and transfer of latent energy to the atmosphere if the winds over the Gulf remained very light and a thin sheen of oil formed on the surface. The thin sheen would significantly reduce the evaporation where it existed, although since evaporation is an energy transfer from the water to the air, it would leave more energy in the water. However, the lightest oil that would form the thin sheen seems to be dispersed pretty rapidly by wind driven waves and mixing in the upper layer of the Gulf of Mexico. If a hurricane with high winds moved over the spill, the large wind driven waves and oceanic mixing would disperse the oil in the upper levels and the fluxes of energy and water vapor would probably not be affected significantly.
There are others who know more about emissivity and albedo than I do, but I have the sense that the amount of solar radiation absorbed by the Gulf of Mexico is also unlikely to change significantly. Depending on the concentration of the oil at various depths in the water, the location of the absorption of solar radiation might change in the water column, but the total amount of energy absorbed by the column probably won’t change much. The relatively small redistribution of energy within the column will likely be dwarfed by the pre-existing Loop Current and the warm eddies shed by that current. To give you a feel for the size of those features, the Loop Current which transports very warm water from the Caribbean Sea into the Gulf of Mexico before looping around Florida and merging with the Gulf Stream, is roughly 800 meters (2600 feet) deep and 200-300 km (125-200 miles) wide. It contains a lot of stored energy to fuel hurricanes. The warm eddies are typically about 80-150 meters (500 feet ) deep. Those features will play a much more significant role in the intensity of any hurricane passing over the region than the oil spill will.
One way in which the emissivity of the oil will possibly effect our analysis of what is going on in the Gulf is in the satellite derived Sea Surface Temperatures (SSTs). Those SSTs are based on algorithms that assume the effective radiative surface is sea water and not a mixture of sea water and oil. So, they may produce erroneous estimates of the SSTs. Fortunately in the Gulf we have buoys and other locations that also measure SSTs and so we should be able to correct for any problems that the oil produces.
That’s my two cents worth on how the oil spill might effect hurricanes. The ecological effect of a hurricane producing a storm surge that drives the oil into bays and estuaries is another matter entirely, but that’s not my area of expertise.