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Posted at 11:00 AM ET, 08/28/2008

Gustav Grows Again; Hello Hanna

By Jason Samenow

Satellite image of tropical storms Gustav (left) and Hanna (right). Courtesy NOAA

After taking a serious beating over mountainous Haiti, Gustav has recovered remarkably over the deep, warm waters of the northwest Caribbean. In 12 hours, it has strengthened from minimal tropical storm to near-hurricane intensity. While intensifying, Gustav shifted surprisingly south, and is headed for Jamaica, where hurricane warnings are in effect. Meanwhile, we now have tropical storm Hannah in the Atlantic.

Keep reading for more on Gustav and Hanna, and an interactive tracking map. For local weather, see our full forecast as well as NatCast and SkinsCast for tonight's games.

The latest track guidance takes Gustav on a northwest track through the Caribbean and Yucatan Channel into the central Gulf of Mexico late Sunday. Landfall possibilities range from eastern Texas to the Florida panhandle early next week. New Orleans remains near the center of model forecasts. But the region in the track bullseye now may well shift with landfall still four days away and the uncertainty in these forecasts. Having said that, the city of New Orleans is making the right move by starting to plan for a hurricane landfall now.

Gustav's strengthening trend should slow or even reverse as it interacts with Jamaica, but should resume in earnest once it's over the open Caribbean and possibly interacts with the super warm loop current in the southern Gulf of Mexico. The intensity forecast becomes more uncertain as Gustav approaches landfall early next week, but weakening is more likely than strengthening. However, modest weakening of a possible major hurricane may be little consolation to the whatever location Gustav happens to strike.

Tropical storm Hanna is forecast to track northwest towards the northern Bahamas over the next five days. This storm should become a hurricane, and possibly an intense one. It's too early to say whether it will impact the U.S. East Coast. As it draws closer, the National Hurricane Center indicates the steering flow could weaken causing Hanna to meander for a while, or it may be swept out to sea by a front moving off the East Coast...

Track Gustav, Hanna and several other areas of disturbed weather in the tropics, using the interactive map below.

Powered by hurricane-tracking software from Pan, zoom, and click on points along the storm's projected track for intensity forecasts.

By Jason Samenow  | August 28, 2008; 11:00 AM ET
Categories:  Tropical Weather  
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I always get this mixed up, but--isn't a hurricane more powerful on the east side of the landfall spot than on the west side?

Posted by: mcleaNed | August 28, 2008 11:33 AM | Report abuse

@mcleaNed: I think the storm surge is usually greater on the east side of the storm, as the rotation of the storm (and thus wind direction) is pushing water towards the shore. I'm not sure if there is any difference in wind speeds, just wind direction.

Posted by: Southside FFX | August 28, 2008 11:37 AM | Report abuse

Ned--Yes. Usually the right side...or whatever side coincides with the direction of storm motion and the storm's counter-clockwise circulation.

Posted by: Capital Weather Gang | August 28, 2008 11:40 AM | Report abuse

remember a couple weeks ago when Hagee asked people to pray for horrible weather in Denver for Obama's speech? looks like God had other ideas

Posted by: hello | August 28, 2008 11:59 AM | Report abuse

i take that back. it was Focus on the Family.

Posted by: hello again | August 28, 2008 12:04 PM | Report abuse

Models are in fairly good agreement as to Gustav's track. They take the storm past the western tip of Cuba and into the Gulf, but after that... agreement= not so much.

Interesting how the GFS takes Hanna out to the right.

Posted by: Model Monkey | August 28, 2008 12:07 PM | Report abuse

Note to Mike: Pressure depth does not increase wind speed; pressure gradient does. Generally, the closer or more "tightly-packed" the isobars, the higher the winds. Systems at greatest deviation on either side from the normal sea-level pressure of 1016 hectopascals [millibars] will tend to have the greatest wind speeds where pressure gradients are steep. At the center [eye] of the cyclone [e.g. central pressure 885 hPa] or anticyclone [e.g. central pressure 1052 hPa] winds will generally be light or calm. In between systems, there could be a pressure gradient as high as, say, 200 hPa over 350 miles; in this area of steep rise or fall of pressure, the wind speed is high. Generally, the faster the barometer rises or falls, the higher the expected wind speed. When the barometer is very low or high, there may be higher winds as pressure equalizes towards the normal sea level value, but that is not always the case since the pressure may equalize more slowly than normal.

Posted by: Anonymous | August 28, 2008 12:08 PM | Report abuse

As I wrote yesterday, the models do not deal well with land interaction/intensity shifts exemplified by the shift south into Jamaica yesterday. Until this thing crosses the western part of cuba, the path and intensity of impact on US is completely a guess. Larger storms can make their own steering currents. This storm is also moving much slower than predicted, so the steering factors may change with the pushedback time of impact.

Posted by: Jamming | August 28, 2008 12:43 PM | Report abuse

Anonymous, I understand how wind speed is connected to pressure gradient. My question was:

1. Is the pressure around Gustav low enough that 983mb is truly a tropical storm or is it more likely a hurricane

2. Can reconnaissance planes accurately measure wind speed (can they sample enough points to account for storm asymmetries) or is pressure a more reliable measurement of storm strength.

Posted by: Mike | August 28, 2008 12:43 PM | Report abuse

To Mike:

Pressure isn't the best measure, because you have to take into account the ambient/average pressure of the environment. It's the relative pressure (and as stated, the gradient) that's indicative of the storm's true strength. This is especially evident when comparing storms in different basins (pacific versus atlantic for example) where the ambient surface pressure is different.

2. By using recon planes (dropsondes) as well as satellite derived wind products, they get a pretty good handle on the storms actual intensity.

Posted by: D | August 28, 2008 12:54 PM | Report abuse

is the storm named hannah as in the post or hanna as in the interactive map?

Posted by: sam | August 28, 2008 3:24 PM | Report abuse

Sam, no H at the end apparently. The new EURO continues to be troubling... has Hanna moving just south of FL and eventually into the New Orleans areas a a major hurricane.

Posted by: Ian, Capital Weather Gang | August 28, 2008 3:36 PM | Report abuse

Flying planes into hurricanes must be the most exciting meteorology job available.

Posted by: mcleaNed | August 28, 2008 3:48 PM | Report abuse

mcleaNed: You can have the hurricane hunter job. I've flown over 20 times in the last 10 years (just to visit my dad in SC, too), and after one incident we had over NC, I couldn't imagine doing that. We flew through a storm in North Carolina, and we hit an air pocket and dropped about 100-200 feet and immediately gained the altitude back. Everything flew around and people were screaming and drinks went spilling and flying. Holy crap it was scary...

Oh, and CNN reports that Gustav has made landfall in Jamaica with 70 MPH winds.

Posted by: weatherdudeVA | August 28, 2008 4:40 PM | Report abuse

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