Wednesday, May 22, 2013

Professor Quibb's Picks-2013

My personal prediction for the 2013 Atlantic hurricane season is (written May 20, 2013):

18 cyclones attaining tropical depression status
16 cyclones attaining tropical storm status
9 cyclones attaining hurricane status
4 cyclones attaining major hurricane status

These predictions are slightly above normal for an Atlantic hurricane season, particularly in the hurricanes category.

The last decade or so has constituted by far the most active such period in known history for tropical cyclone formation. This may reflect a long-term cycle in Atlantic tropical cyclone activity, known as the Atlantic Multidecadal Oscillation (AMO). The AMO could theoretically explain, for example, the lull in formation in the 1980's and the recent surge in the 2000's.

However, the state of the El Nino is fairly neutral. It is fairly unlikely that a strong El Nino or La Nina event will develop significantly before the conclusion of this year's hurricane season. A neutral state of the ENSO would suggest a fairly average season. This reasoning, coupled with the fact that the Altantic basin is still in a long-term active period, suggests a slightly above above normal hurricane season.

Finally, sea surface temperatures near the U.S., especially near the Gulf Coast, are below normal, and well below where they were in May 2012, partially stemming from a much colder winter and early spring across several areas of the country. Favorable conditions may then be slow to reach areas near the U.S., though this of course does not exclude powerful mid- or late-season storms.

Below, my anticipated risk factors for four major regions of the Atlantic basin are listed. The risk index runs from 1 meaning very low potential to 5 being very high potential.

U.S. East Coast: 3
Though the Bermuda High is still far to the east, near the Azores, small blocking ridges may be frequent in the western Atlantic, so tropical cyclones could very well be steered towards the east coast. Again, such an event is unlikely towards the beginning of the season due to cooler waters and anomalously high wind shear, but the risk near the end of the season is higher.

U.S. Gulf Coast/Northern Mexico: 2
The Gulf of Mexico has not only been anomalously cool, but also the jet stream has dipped well into the U.S. Midwest over the first few months of this year. Such events cause disturbed weather to be frequent, but generally inhibit cyclone formation. As such, the Gulf coasts of U.S. and Mexico are relatively protected, though there is still potential for a sufficiently powerful cyclone to track through the Gulf and make landfall. Also, Florida is at an above average risk, despite the low Gulf index overall.

Yucatan Peninsula and Central America: 3
As usual, the Yucatan and surrounding areas can expect some tropical cyclone activity, particularly in the form of weak systems. The eastern Atlantic is warm and conditions will be favorable for the development of tropical waves before such waves enter the southwestern Caribbean, so stronger storms will almost certainly track to the north.

Caribbean Islands: 5
It has been a few years since a "traditional" Cape Verde hurricane has formed in the east Atlantic and stayed on a westerly path over the Caribbean Islands. However, the likely development of temporary ridges over the tropical Atlantic would push even strong hurricanes on such a path. The strongest cyclones of the season are likely to come over, or pass close to, these islands.

Overall, a slightly above average 2013 season is expected, with particular risk to the Caribbean Islands and the southeast U.S.. Since the climate of the Atlantic region is less volatile than last year, there may be fewer meandering storms such as Hurricane Nadine, and fewer unusual jet stream interactions, such as the one which caused Hurricane Sandy to make landfall in the northeast.

1 comment:

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