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Tropical Depression #9 Could Impact Our Weekend

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The 72 hour forecast for Tropical Depression #9 as of 8/21 at 2 p.m.  (Source: Google Maps)

The 72 hour forecast for Tropical Depression #9 as of 8/21 at 2 p.m. (Source: Google Maps)

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MIAMI (CBS4) – Less than 24 hours after entering the peak of annual Atlantic Hurricane Season (Aug. 20th – Oct. 1st) there is a system which could threaten South Florida as early as this weekend.

Tropical Depression 9, which may become Tropical Storm Isaac at anytime, is now racing westward across the open waters of the tropical Atlantic. As of 2 p.m. on Tuesday, the system was located about 500 miles east of the Lesser Antilles.

The storm was still a large distance away and there were many unanswered questions.

The bottom line, according to CBS4 meteorologist Jeff Berardelli, is that at this point the consensus of the best computer models show the storm strengthening and moving in the general direction of Florida.

Waters are plenty warm, wind shear is mainly weak (high wind shear typically tears tropical systems apart) and dry air, although present around the system, is not copious, thus there is little reason this system won’t eventually strengthen. The main limiting factor in the short-term is the forward motion of the system itself which is 20 mph. That is expected to slow in about 3 days. So at this point we do expect this system to gradually strengthen to a hurricane, according to Berardelli.

So which way will it go?

As of now there is a deep ridge north of the storm over the central Atlantic. This ridge is very typical and every season this ridge steers systems on its south side toward the west (towards the Caribbean). At the present time the ridge extends through Florida into the Gulf of Mexico and if there was a storm to our south right now it would likely act to protect us.

This ridge will remain in place until late week. But once the storm reaches the central northern Caribbean the ridge will begin to weaken and recede into the Atlantic Ocean. This weakening will be caused by a trough of low pressure, a dip in the jet stream, currently centered near New Orleans.

The dip will move east slowly and dislodge the protective ridge over South Florida. At this point, later in the week, the storm will begin to slow and respond to the “weakness” in the ridge. With this weakening protection, the storm will also begin to turn to the northwest. This general scenario seems fairly certain. And the timing of the players in this scenario also seems fairly straight forward.

The devil is in the details here.

So the questions that remain are exactly when will this turn occur and will the storm move across the mountains of the Greater Antilles like Hispanola? Those of us familiar with living in Florida understand that many times in the past those islands helped protect South Florida to some extent by acting as a barrier and causing systems to weaken some. We here in South Florida certainly can not count on this and small changes in track can make a huge difference in intensity.

So here are the important details to take from this.

The system is likely to strengthen.
South Florida is in the center of the computer model guidance late in the weekend and early next week.
Currently there is no way to tell whether the storm will directly affect us or miss us by a marginal distance.

So what should you be doing?

At this point you should be making sure your hurricane supply kit is complete and anything out of date is replaced. Also you should be going over your hurricane plan with your family. No other action is necessary at this juncture. But have your plan and personal life in order within the next two days. Check back with us at CBS4 and CBSmiami.com and we will keep you updated on the changes. If you are required to take action it could be as early as Friday or Saturday.

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