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Tropical cyclone season underway

Jun 14, 2016

The start of the Atlantic hurricane season was June 1, and in the eastern Pacific the season began on May 15. Last season the presence of a strong El Nino pattern in the Pacific led to a quieter season in the Atlantic but a rather robust season in the Pacific. The El Nino is now gone, and a La Nina pattern may develop as early as late summer. This is a situation where sea surface temperatures in the equatorial Pacific run below normal as opposed to the above-normal temperatures of an El Nino pattern. A neutral pattern will likely prevail over the next several months, and this usually means a more active Atlantic hurricane season and a less active eastern Pacific season.

So far, this has been the case, although it is still very early. In the Atlantic, tropical cyclone activity developed even before the official start of the seas. In fact, a very unusual system arose in January this year when a strong low in the subtropical eastern Atlantic became a subtropical storm, and then evolved into the first hurricane of the season. Hurricane Alex impacted the Azores before it lost its tropical characteristics. It is quite rare for a hurricane to develop in January in the Atlantic. The last time it occurred was in 1938. There was a hurricane in 1954 that developed in December and lasted into January of 1955.

Since Alex, there have been two additional tropical cyclones in the Atlantic basin. Bonnie developed in late May prior to the start of the season off the southeastern U.S. coast, then moved to near the Carolina coast and produced some very heavy rain in that region. The system lost its tropical characteristics after it moved inland for a couple of days, but regained tropical storm status near Cape Hatteras before weakening after it moved east of the Gulf Stream a couple of days later.

Tropical storm Colin developed in the Gulf of Mexico in early June and moved across northern Florida and into the southeastern U.S. coastal waters where it lost its tropical characteristics and moved quickly northeast over the western Atlantic as a strong non-tropical low.

In the eastern Pacific, so far only one system has developed, a tropical depression near the southern coast of Mexico that moved inland within a couple of days in early June. It produced some heavy rain, but its winds never reached tropical storm force.

There are other influences on tropical activity in addition to the El Nino/La Nina cycle. Wind conditions over Africa have an impact on Atlantic systems, and the pattern of sea surface temperatures impacts all oceans. There has been a rather persistent area of colder-than-normal sea surface temperatures in the Atlantic south of Greenland, which has been referred to in the mass media as the “Cold Blob” of the Atlantic. If some of this colder water could be transported to tropical latitudes, it could serve to suppress tropical storm formation despite the presence of other favorable conditions. It could also impact the pressure pattern in the Atlantic, perhaps leading to stronger upper level winds in the tropics — winds that can be an inhibiting factor for tropical cyclone formation. For these reasons, despite the lack of an El Nino, most of the seasonal forecasts for the Atlantic are for a near normal season in terms of the number of tropical cyclones that form, which would mean more activity than 2015, a below-normal season. For the eastern Pacific, most forecasts are also expecting a near normal season, but in this case, this would be a less active season compared with last year.

To read the full NOAA seasonal forecast, use the following link: http://www.noaa.gov/near-normal-atlantic-hurricane-season-most-likely-year.

Passing of a pioneer
When it comes to seasonal predictions of Atlantic hurricane activity, Dr. William Gray of Colorado State University was a true pioneer in his field. Dr. Gray, who passed away in April of this year, founded the Tropical Meteorology Project at Colorado State. This program was the first to issue seasonal outlooks of tropical storm activity.

Gray was the first to document a correlation between the El Nino/La Nina phenomena and hurricane activity in the Atlantic. His research also identified other parameters that correlate with Atlantic hurricane activity, and by combining all of this data, he and his colleagues demonstrated significant skill in a very difficult forecast problem and advanced the understanding of tropical cyclones in general. His team continues the work that he began.

Use the following link to access the Colorado State Tropical Meteorology Project website where many resources can be accessed, including the most recent seasonal hurricane forecasts: http://tropical.atmos.colostate.edu/Forecasts/.

This is a good time of year to review your hurricane preparedness. Whether a hurricane season is above normal or below normal is immaterial if a storm impacts an area of interest to you. If you have not visited the National Hurricane Center website recently, you should take the time to do so (http://www.nhc.noaa.gov). The site has been recently redesigned and there is more information available than ever before. Exploring the website will make you more familiar with the products and information that are available, which will put you in a better positions to quickly access what you need if a threat arises for your area.

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