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  • Writer's pictureBryan Norcross

Grace is speeding through the Caribbean and Fred isn’t done yet

The news is good on Tropical Storm Grace. Although we should remember the people in the Dominican Republic, which is in its path. Parts of that country were just flooded by Fred. And Haiti will also be affected, where people are dealing with yesterday’s powerful earthquake.

The disorganized storm is speeding west just south Puerto Rico. Rain bands with gusty winds and tropical downpours will rotate across the Virgin Islands, Puerto Rico, and the nearby islands today. Flash flooding and mudslides are possible from continuous heavy rain falling on the mountainous terrain.

Grace will be past Puerto Rico tomorrow morning, and is aimed directly at the Dominican Republic mountains, just like Fred was last week.

As we saw with Fred, mountains can debilitate the circulation of a tropical storm, and they are expected to do that to Grace as well. The unknown is whether Grace will slam into the 10,000-foot, storm-shredding mountains head-on like Fred, or whether enough of the storm skirts around the tallest peaks to the south to live for another day.

After the Dominican Republic and Haiti, Cuba is dead ahead. If Grace survives its bout with the giant mountains, and then what’s left of it takes a track something like what’s shown in most recent National Hurricane Center cone, it’s only chance to reintensify would be to track along the right side of the cone over the water.

Grace is a small storm with a disorganized core, which mountains and rough terrain will likely affect much more than if it had a large, well-defined circulation. So a little difference in path makes a big difference in intensity. We’ll have to wait a couple of days to be 100% sure that Grace is seriously disrupted by these mountains before we feel good that it’s not going to be a significant threat to Florida.

The other factor in play is the upper-level winds. Several of the various computer models predict that they will be reasonably conducive for strengthening, so it’s the mountains that would seem to be the most important player at the current time.

In this kind of situation, it’s important to remember that all forecasts for disorganized or developing storms have larger errors than those for strong hurricanes. It’s especially important not to lock in on today’s cone, or any cone when the storms center is not well defined.

At this time it doesn't appear likely that Grace will be a big threat, but we still have to keep in mind that there's a chance that Grace could threaten South Florida as early as late Wednesday if it somehow survives its trek over the mountains and heads toward the state. In any case, some parts of South Florida will likely get some heavy rain with gusty winds as it goes by.

Tropical Storm Fred lives again. The storm has reorganized in the Gulf, and is heading toward landfall in the Florida Panhandle late tomorrow or tomorrow night as a moderate tropical storm. A Tropical Storm Watch is in effect.

The biggest threat from Fred appears to be from the rain. The intense conveyor belt of tropical moisture that was forecast to stream over the Florida Peninsula, is now projected to stay over the Gulf, but impact the Panhandle to the right of where Fred’s center comes ashore. Rainfall could exceed 5 inches and a Flash Flood Watch has been issued. The heavy rain will spread across the Southeast as well.

Fred was a poster child for the challenges of communicating the forecast in a situation where the storm is highly disorganized. We use the same system – the cone and various forecast products – to describe where the system is going to go for a hurricane and a messy tropical depression. Even though we know that the forecast for the depression is much less certain.

Fred’s track farther west – away from peninsula Florida – was suggested by some of the computer forecast models on occasion, but the typically most reliable computer forecast aids failed to pick it up.

All of this is a good lesson as we look at Grace coming along a similar path. There is no guarantee that the outcome will be the same as with Fred, just that there’s always a decent chance it won’t be exactly what was originally forecast.

Elsewhere in the Atlantic, there’s a small disturbance near Bermuda that has a slight chance of developing before it gets swept out to sea. Significant impacts on land aren’t expected.


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