An Active 2010 Hurricane Season

By now, most people have heard the bad news. The 2010 hurricane season is shaping up to be a very active one. Our forecast of 18 named storms with 11 hurricanes and five major (Category 3, 4, or 5) hurricanes is not much different from the other forecasts. But how does that compare to past seasons? If we take into account the several storms per season that were likely missed prior to the era of satellite and modern reconnaissance, then from 1950-2009 the average number of named storms per season was near 12, with six hurricanes and two major hurricanes. With a prediction of 18 named storms, we are forecasting at least a 50% increase over a normal season.

The five seasons with the most named storms in the past 100 years were 1933 (21), 1969 (18), 1995 (19) and 2005 (28). A total of 18 named storms would tie this year in third place (with 1969) most named storms in a season in the past century. With so many major hurricanes forecast for 2010, it seems unlikely that the islands of the Caribbean and the U.S. Coast will escape a major hurricane landfall in 2010 as they did last season. Although we cannot forecast months in advance the paths that all of the hurricanes will take, we can use some of the same weather and ocean parameters that are used to predict seasonal storm totals to provide insight as to where the hurricanes may tend to track over the coming season.

Analog Years

Previous seasons with a similar setup of ocean temperatures and atmospheric flow patterns to what we’re seeing now across the tropics include 1958, 1966, 1969, 1995, 1998 and 2005. We call such seasons “analog years.” Analog years can provide valuable insight as to where storms might form or track in the coming season. In Figure 1, I’ve plotted all of the hurricanes that formed in those six analog years.

 Higher Risk Areas

It’s a busy map, but it does show a pattern of tracks and impact areas. For example, in most of the analog years, the Northeast Gulf Coast was impacted by a hurricane, and often a major hurricane. Secondarily, the islands of the northern Caribbean were impacted quite often in the analog years. The final region of greater impacts is along the coasts of South and North Carolina. Given the predicted weaker-than-normal Bermuda High this summer, I think that the analog seasons do indicate some of the areas likely to be hit by a hurricane this year. With that in mind, we have constructed a map that highlights the regions of increased risk of a landfalling hurricane this year (Figure 2).

As can be seen in Figure 2, the highest risk areas (in red) encompass all of the islands of the northern Caribbean Sea from St. Lucia to western Cuba, the Bahamas, southern Florida and the Northeast Gulf Coast. In addition, the coasts of South and North Carolina and the northeastern Yucatan Peninsula would be at high risk of a hurricane landfall. The analog years don’t indicate a significantly increased risk to the Texas Coast, or to the Northeast U.S. Coast from Virginia to Maine. But with high pressure forecast to dominate the Central U.S., it’s possible that hurricanes entering the Gulf might get steered more to the west, impacting the coast of Mexico in the western Gulf.

Now this doesn’t mean that if you live along the Texas Coast or in the Northeast U.S. that you can breathe a sigh of relief. Analog years only provide guidance as to those areas with a potentially higher risk of landfall. The risk of
a landfalling hurricane in Texas or in the Northeast U.S. is certainly not reduced
below the level of a normal hurricane season. Steering mechanisms are always
changing through the season. It all comes down to just what steering pattern is
there when each hurricane forms. No coastal area can be declared safe from a hurricane landfall.

Oil Spill Impact

It doesn’t matter where I’ve spoken over the past month, the one question that I always get at the end of my talk concerns the potential impact of the oil spill on the hurricane season. Most people want to know either how the oil spill might affect a hurricane’s formation, intensity or track, or how a hurricane might impact the oil spill itself.

Let’s address the first issue, how the spill might impact a hurricane. There are various theories circulating that the oil might help to heat up the northern Gulf of Mexico, creating an environment more favorable for intensification, or that the oil sheen on the surface will prevent the evaporation of water that the hurricane needs for fuel, causing it to weaken or not develop in the first place. While I could believe that an oily sheen on the surface might inhibit water evaporation enough to hinder the initial development of a small tropical disturbance, the sheer size of a typical hurricane when compared to the relatively small size of the oil spill makes me think that the hurricane won’t even notice the oil spill as it passes on by.

For comparison purposes, I’ve overlaid the current size of the main oil sheen area atop a satellite photo of Hurricane Gustav in Figure 3. Gustav was an average-sized Category 2 hurricane at the time. As you can see, the size of the oil spill is dwarfed by even an average-sized hurricane. A hurricane draws
in energy from hundreds of miles around the center, even outside the outermost bands of squalls. So it’s very unlikely that any passing hurricane’s intensity or track might be influenced by the oil spill, even if the oil spill were to double in size by the peak of the hurricane season.

As to the other question – how a passing tropical storm or hurricane might impact the oil spill – that’s a subject of great debate among scientists. Most agree that a passing hurricane’s strong wind and rough seas would very quickly break up and disperse the oil slick, allowing the oil to be more quickly consumed by oil-eating bacteria that live in the oceans. That’s a good thing. But the big question is, could a passing hurricane push some of the oil into the coastal areas and even inland? Let’s try to break down the potential impact into its components.

First of all, there are the strong winds and rough seas. Even “milder” tropical storm conditions developing in the area would force the containment and cleanup efforts to be abandoned and the area evacuated. The oil containment booms and any coastal barricades of sand that have been constructed would likely be displaced or destroyed, increasing the risk that oil would impact the coastal areas. And if the hurricane passed over or to the west of the oil spill area, the storm surge could carry water contaminated with oil several miles inland, leaving an oil-contaminated field of debris.

But if the hurricane was to pass to the east of the oil spill, the effects could actually be beneficial. Northerly winds west of the hurricane could help to break up and push the oil away from coastal areas. And for that possibility, there is a precedent we can look at. On June 3, 1979, the Mexican platform Ixtoc 1 blew out in the Bay of Campeche, dumping more than 140 million gallons of oil into the Gulf of Mexico. That’s nearly 10 times the amount of oil spilled into the Gulf by the Deepwater Horizon blowout. In September of 1979, Hurricane Henri formed in the Bay of Campeche not far from the oil spill. As the storm passed, beaches along the Mexican coast that had been covered with oil were scoured and cleaned of most of the oil. But even though it’s possible that a passing hurricane could have some beneficial impact on the oil spill, the negative overall impact of the hurricane would most likely outweigh any possible benefits.

When Will the Season Begin?

The final question to answer involves the predicted start of the 2010 hurricane season. When will the first storm form? Will they develop one after the other from mid-June as they did in 2005? Or will activity gradually increase, reaching a peak the second week of September, as would be expected in a typical season? I think that the answer lies somewhere in between those two extremes. Wind shear across the tropics is already anomalously low for early in the season. And with water temperatures at near-record-high levels, I think that there’s a good chance that from one to three named storms will form during June and July. Early season storms typically impact the Caribbean Sea and/or the Gulf of Mexico, and there’s no reason to think that this season will be any different. We may have to deal with a potential tropical threat to the Northern Gulf Coast sooner than we’d like. The bottom line for the 2010 hurricane season is that all preparations should be completed as soon as possible. The clock is ticking for what looks to be a very bad hurricane season. CI