Hurricanes Reanalysis: A Game of Thrones

April 23, 2014

Earlier this month at the American Meteorological Society's Conference on Hurricane and Tropical Meteorology, there was discussion of three storms in particular that will probably have some impact on the perception of hurricane risk in both the Atlantic and Pacific Ocean Basins.

Let's begin with Hurricane Camille, which destroyed a part of the Gulf Coast over 40 years ago. For a long time, it was believed that Camille made landfall with a central pressure (Cp) of 909 mb and 1-min sustained winds of 190 mph-which made it the strongest hurricane to make landfall in the U.S. But thanks to some great detective work reanalyzing the original observations, the storm has been downgraded to 175 mph (albeit with a lower Cp of 900 mb). This effectively de-thrones Camille, making it just the second strongest landfalling hurricane in U.S. history behind the Great 1935 Labor Day Hurricane.

Fast forward to Fall of 2012. Another storm discussed was-you guessed it-Sandy. At least two of the presentations noted that while the storm track was, at least initially, difficult to forecast in terms of the left hand hook, it tracked similarly to storms in 1893, 1938, and 1954 (Hazel). While these storms did not execute a left hook, they all caused devastation across the mid-Atlantic states, the Northeastern U.S., or Canada.Additionally, given the high density and value of the exposure where Sandy made landfall, it did not take more than Category 1 winds (and concomitant storm surge at high tide) to do the damage it did.

That left hook was caused in part by interaction with an approaching extratropical cyclone (or trough) from the west-a perfectly normal occurrence for that time of year in mid-latitudes. Most meteorologists readily accept that it was a very explainable Fujiwhara effect that resulted in the left hook rather than global warming and melting polar ice.

Sandy was unique only because of the relatively short historical record of hurricanes in the U.S., which is exactly why companies like AIR Worldwide develop risk models that more accurately put such storms in perspective.

Over to the Pacific Basin, and last November's Super Typhoon Haiyan. The Joint Typhoon Warning Center "measured" Haiyan with 195mph winds at landfall in the Philippines. But most everywhere in the world (except for the North Atlantic), tropical cyclone wind speeds aren't so much measured as deduced-using a satellite 22,300 miles up, which looks at the temperature and height of clouds to estimate intensity using a modern form of the Dvorak Technique. While the original technique relied on meteorologists subjectively evaluating cloud patterns, the modern version is supposed to be completely objective. Sometimes human feelings still get in the way.

When Super Typhoon Tip developed 190 mph winds in 1979, it set the benchmark for the strongest typhoon ever. On several occasions since, even though the technique has yielded objectively stronger typhoons, hurricane experts were reluctant to top Tip. When Super Typhoon Megi hit the Philippines in 2010 for example, reconnaissance aircraft readings were available because of an ongoing Hurricane Field Project. Even though these readings legitimately exceeded Tip's maximum winds, Megi winds were set just a bit lower-because nobody wanted to top Tip.

However, after Haiyan, the evidence was perhaps too strong.Hurricane experts finally decided to give the crown for strongest tropical cyclone ever to Haiyan. Tip's record has finally been broken, but Haiyan's coronation is also significant because hurricane analysts will likely re-visit some previous near-record strong storms in the Pacific, as they have been doing for the Atlantic. This may result in more storms topping Tip, if not Haiyan, and that will certainly change the perception of tropical cyclone risk in the Pacific. Stay tuned for more reanalyses!

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