Atlantic Hurricane Season Underway
June 4, 2009, 9:54 am
Filed under: world news

June means the start of the Atlantic Hurricane Season. The Atlantic Basin is relatively quiet at this time. If there is going to be any development this time of year you would look in the Gulf of Mexico eastward to near the Bahamas and the western Caribbean. No immediate development is likely just an area to watch next several days for possible enhanced rainfall Florida Panhandle to southern Alabama and southern Georgia. Meanwhile, weak low pressure south of Mexico in the eastern Pacific with disorganized showers and thunderstorms is not expected to develop or organize. There is a non tropical low about 400 miles north-northeast of the Azores that is producing showers and gusty winds to near gale force. This system is drifting northward into cooler waters and has a very low chance of developing but will bring impact in its path. ———————————— Tropical and Wave Expert Dr. Steve Lyons talks about what it takes to have early season tropical events: How Do I Develop Thee, Let Me Count the Ways Atlantic Basin hurricane season is beginning. So far in 2009 we have almost had a preseason development that had subtropical or tropical characteristics in the northern Gulf of Mexico that deluged Florida, and one this past Thursday off the North Carolina coast that became the 1st Tropical Depression of the season. There have been no names as of yet though. But you might ask, what are some common sources for preseason or very early season tropical cyclone development in the Atlantic Basin? There are a few and it’s easiest to simply list the most common ones and give a few comments on each, so here goes! 1) Upper level low pressure that burrows to the surface within showers and thunderstorms 2) Frontal boundary that drops into the Gulf of Mexico or off the southeast U.S. coastline 3) Strong mesoscale convective complex that dives from the tornado haven of the SW and/or plains into the Gulf of Mexico For type (1); often in late spring upper level troughs of low pressure dive south into the Gulf of Mexico or into the Bahamas or southwest tropical or subtropical Atlantic. These can be very intense at twenty to forty thousand feet and can cause a large mass of showers and thunderstorms to form along their eastern flanks. If they persist over tropical or subtropical waters they can at times begin to develop showers and thunderstorms that are more widespread and the mid and upper level low pressure begins to descend to the sea surface and form low pressure there. If showers persist and they are collocated with an area of surface low they can eventually become a subtropical or tropical cyclone. For type (2); it is not uncommon in late spring for a strong or vigorous cold front to blast into the Gulf of Mexico and/or off the southeast U.S. coastline. Fronts tend to have spin that is the same as a low area along them and on occasion weak low pressure will form on one of these fronts and then strengthen should showers and thunderstorms flare up near that low pressure area. Most of the time upper winds are fast and not favorable for subtropical or tropical cyclone development along this frontal low at lower latitudes, but should one persist and upper winds eventually (2-3 days later) lighten, conditions can become favorable for that low to transition into a subtropical or tropical cyclone. For type (3); we all know that spring and early summer is tornado season. Often large clusters of showers and thunderstorms, called mesoscale convective systems (MCS), develop and move east or northeast. But sometimes they move southeast and dive into the Gulf of Mexico causing a marine hazard. The MCS can and often does generate a spinning mesoscale convective vortex (MCV) at mid-levels, caused by heating from the showers and thunderstorms in the MCS. On rare occasions this MCS and MCV can take on tropical cyclone characteristics if it persists over water and upper winds weaken. These are the 3 primary preseason subtropical and tropical cyclone development agents, and they persist through the start of hurricane season. In fact they can be an initiator during any part of hurricane season, but tend to be the primary initiators before it begins or near its start. So keep an eye out for these three features, and of course we will too here at The Weather Channel. Are you ready for the 2009 Hurricane Season? You should know the difference between a Hurricane Watch and a Hurricane Warning. A Hurricane Watch means that hurricane conditions are possible within the specified watch area within the next 36 hours. A Hurricane Warning means that hurricane conditions are expected to affect the warning area within 24 hours.


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