2PM UPDATE: Chantal is now up to 65 MPH. I've updated the map below to reflect the latest advisory.
In the diary I wrote on Tropical Storm Chantal when the system first formed on Sunday night, I added the following blurb of caution at the end of the post:
Tropical systems have a long history of doing things that forecasters don't expect and models don't pick up on. Interests in the Caribbean and southeastern United States need to keep a close eye on Chantal as it approaches land. These systems have a tendency to strengthen (or weaken) unexpectedly and/or veer off its projected course. Forecasters and models are much better at predicting where the storm will go than how strong it'll be when it gets there.Chantal is no exception. The storm now has 65 MPH winds despite its raggedy appearance, and has a not-insignificant chance of becoming a hurricane before it makes its first landfall on the Dominican Republic side of Hispaniola early tomorrow morning. Hurricane watches are in effect for the southern and eastern side of the Dominican Republic to reflect this possibility.
The forecast track for Chantal surprisingly hasn't altered much since the initial advisory a few days ago. The greatest uncertainty right now (in both track and intensity) is what will happen with the storm after it interacts with the high terrain of Hispaniola. The storm is still moving pretty swiftly (WNW at 29 MPH as of 2PM) in the strong easterly winds along the southern edge of the high pressure over the central Atlantic Ocean, so there's a good chance that Chantal will speed over Hispaniola without being shredded apart too much by the mountains.
The speed at which Chantal is moving is also hindering intensification, as it's pushing the center of circulation away from the deep convection (thunderstorm activity) within the storm itself. Storms need their center of circulation very close to the deep convection to sustain themselves and strengthen.
The models have been pretty consistent in that Chantal will slow down and turn to the west-northwest (towards the southeastern United States) by the weekend as the high over the Atlantic weakens and stops steering the storm like it is now, but they're diverging on where this will happen.
Here's the spaghetti plot from this morning's model runs, showing the general west-northwesterly turn expected as Chantal reaches the Bahamas by the weekend:
The storm is likely at its strongest right now (though it may tick up a little bit) and will undergo weakening from there. The National Hurricane Center's 11AM discussion had this to say regarding intensification:
THE UPPER-LEVEL WINDS ARE FORECAST TO REMAIN UNFAVORABLE IN THE AREA OF THE BAHAMAS FOR SIGNIFICANT DEVELOPMENT...AND ONLY SMALL STRENGTHENING IS ANTICIPATED AFTER THE CYCLONE CROSSES HISPANIOLABarring any unforeseen strengthening as the system approaches the United States, the big issue will be rainfall more than wind. Since the storm will be out of the steering influence of the high pressure over the Atlantic, it's going to move very slowly once it reaches the Bahamas and starts to interact with the southeastern United States.
Below is the rainfall forecast from the Weather Prediction Center (formerly Hydrometeorological Prediction Center) for the next 7 days. A wide swath of 2-3+ inches of rain is expected over the southeast, with more possible in localized areas. Expect this map to change as the system gets closer to land. It's also worth noting that this is total rainfall over the next 7 days, taking into account any typical summertime thunderstorms that form over the southeast.
If you live in (or are visiting) the Greater Antilles, you need to take immediate precautions to protect your life and property. Y'all are pros at this. Those of us in the southeastern United States need to keep an eye on Chantal as it approaches us this weekend. It's still far enough away that anything can happen, so check in with the NHC once or twice a day, at the least.
You can follow updates on Chantal and other tropical systems in the Atlantic and western Pacific over at the National Hurricane Center's website, and you can follow me on Facebook for other tidbits of weather information if you'd like.