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Isaac remains a tropical storm, hurricane warnings in effect

Posted by David Epstein  August 27, 2012 05:00 PM

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Late this afternoon Isaac remained a strong tropical storm but has not yet reached hurricane strength. Isaac is forecast to move closer and closer to the Gulf Coast over the next day and also become a hurricane. Best estimates are for the storm to be a category 1 storm when it makes landfall near New Orleans, Louisiana on Wednesday. Wednesday also marks the 7 year anniversary of when Katrina hit. I am not forecasting a repeat of Katrina. There are several reasons a repeat of 2007 isn't likely. First, Isaac is not forecast to be as strong as Katrina. Also, much has changed both in infrastructure and public policy since that storm hit New Orleans. Isaac has not reached hurricane strength partly because of its large size. This might seem counter intuitive but it does make sense. Isaac is like a skater spinning with their arms extended. In order for the skater to gain speed, they must pull in their arms closer to their body. We are waiting for the storm to become tighter and like the skater, put its energy into a small more compact package. For frequent weather updates and more weather information please follow me on Twitter at @growingwisdom
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New England weather
Dry weather continues for the rest of the day across New England. Later tonight and Tuesday a cold front will cross the region and bring the chance for showers. After the showers end, the forecast for New England looks amazing into next weekend. Starting Wednesday there will be sunshine each day through Sunday. It will be in the upper 70s and lower 80s through midweek. Temperatures should turn quite warm (80s to 90F) later this week and to start next weekend. Some of the rain from whatever is left of Isaac could affect us on Labor Day, more on that as we get closer to the weekend.

Current track and projections
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Issac is moving northwestward through the Gulf of Mexico passing offshore along the west coast of Florida. For the next day the track of Isaac is quite certain. However after tomorrow and into Wednesday major wobbles left or right of the track are still possible. The bigger question is what part of the Gulf Coast does Isaac ultimately strike late Tuesday night and early Wednesday. Anyone from New Orleans to Pensacola, Florida needs to be very aware of this storm until it makes landfall Tuesday night or Wednesday. The map above shows the best estimate of landfall and where there are currently hurricane warnings in effect.

What is the cone of uncertainty?

The new buzz phrase seems to be the "cone of uncertainty". If you look at the projected track of the storm or the projected wind field you will notice these predictions start at a point and then widen into a "cone" shape over time. The further out in time a prediction is made, the greater the chance for error. The cone allows meteorologists wiggle room in their predictions and also gives the public a chance to know that even if the exact track is not over their area, there is still some risk. In the image below the darker colors represent those places that are most likely to see tropical storm force winds, the other colors are areas that those winds are possible, but less likely. Everyone in the cone should be listening to the latest forecast. The map was updated early this afternoon.
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How big will Isaac become?
Isaac is large but still having issues becoming organized. There seems to be some dry air getting pulled into the tropical storm and this is having an adverse affect on the thunderstorms that make up all tropical systems. As the storm is in an area of very warm water and more favorable conditions for strengthening we should start to see the winds increase and the pressure fall. Meteorologists are confident the storm will gain strength tonight and Tuesday but uncertainty remains as to how strong the storm will become. Sometimes, if conditions are favorable, hurricanes can go from a Category 1 to a Category 3 in less than a day. Once the storm finally begins to intensify we will have to watch it hour by hour as it approaches the Gulf Coast.
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Republican Convention and the storm
While the storm itself will have limited impact on Tampa and the RNC, the bigger issue I am thinking about is what happens Tuesday and Wednesday. I can foresee a scenario where the storm intensifies to a major hurricane, category 3 or higher and slams into the Gulf Coast. Imagine the visuals of homes destroyed and peoples lives ruined while the Republicans are having their convention. This could end up being a no-win public relations nightmare for the Republicans even thought the storm itself won't hit that part of Florida. The good news is that the strength of Isaac is likely to be such that catastrophic damage doesn't occur. However, we need to watch things closely so stay tuned.

Why do hurricanes form?
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You might wonder why these storms form in the first place. I tell my students that hurricanes are nature's way of moving excess heat from the tropics to the northern latitudes. From about June through October, the oceans in the tropics are very warm. The water temperatures must be in the 80s not only at the surface but several feet below as well. This temperature structure to the sea only happens in the warm months. As the sun evaporates the ocean water that warm moist air rises and can, if conditions are favorable, create thunderstorms. In some cases, these clusters of thunderstorms will group together and begin to rotate. The rotation can be attributed to something called the Coriolis force. The Coriolis is strongest at the poles and zero at the equator. This is why hurricanes don't happen on or within several hundred miles of the equator. (no Coriolis=no spin) Winds inside the thunderstorms stir up more ocean spray which then evaporates and continues to feed the storms. If the winds reach 39 mph, the storm is called a "tropical storm." And when the wind speeds reach 74 mph, the storm is officially a "tropical cyclone," or hurricane. hurricane_needs_sm.gif Once the storm becomes a hurricane they are then categorized into 5 different levels of strength. Category 5 is the strongest and the last time one of those actually hit the United States was in 1992 when hurricane Andrew came ashore south of Miami.

Gardening tip this week

This is a great time of year to plant. I actually feel that for many plants fall is a better time to plant than it is in the spring. Since the ground stays warm well into October, roots have a good chance to become established. When you plant in the spring, much of the energy of the plant goes into making new leaves, not new roots.
If you have a tough spot that you can't seem to grow anything, check out this video and learn about some of the plants that actually thrive in hard to grow conditions.

I'd love to hear your thoughts on this blog or any others. Please follow me on Twitter at @growingwisdom and check out my latest videos at GrowingWisdom.com

This blog is not written or edited by Boston.com or the Boston Globe.
The author is solely responsible for the content.

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About the author

David Epstein has been a professional meteorologist and horticulturalist for three decades. David spent 16 years at WCVB in Boston and currently freelances for WGME in Portland, ME. In 2006, More »
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