Weather Nerd

What will Dolly do? Uncertainty reigns

I mentioned yesterday that it sometimes seems like individual tropical cyclones have distinct personalities, and Dolly’s central personality trait has been “an inability to get her act together,” even when environmental conditions are favorable for strengthening. The 5:00 PM EDT discussion suggests that this trend is continuing:

THE STRUCTURE OF DOLLY APPEARS TO BE UNDERGOING VERY GRADUAL CHANGES. THE OUTERMOST CONVECTIVE BANDS HAVE BEEN WEAKENING TODAY…WHILE CONVECTION HAS BEEN SLOWLY ON THE INCREASE NEAR THE CIRCULATION CENTER. THE RADIUS OF MAXIMUM WINDS IS NOW MUCH SMALLER . . . DOLLY IS HEADED TOWARD A RELATIVE MAXIMUM IN OCEAN HEAT CONTENT…AND IT IS BENEATH A LARGE UPPER-LEVEL ANTICYCLONE THAT COVERS NEARLY THE ENTIRE GULF OF MEXICO. IT SEEMS TO BE TAKING A WHILE…HOWEVER…FOR AN INNER CORE TO BEGIN TO TAKE SHAPE…SO IT IS RATHER UNCERTAIN HOW MUCH DOLLY WILL TAKE ADVANTAGE OF ITS ENVIRONMENT.

One possible scenario is that Dolly might finally get her act together as she gets closer to the coast, and then strengthen rather quickly. This sort of last-minute intensification is a disaster planner’s worst nightmare. However, it appears unlikely that Dolly will ever become a major hurricane — indeed, it gets more and more unlikely with each hour that passes without significant strengthening — so the odds of Texas residents being confronted with an unexpected monster storm seem mercifully slim.

That said, there is a great deal of uncertainty about Dolly’s likely intensity at landfall. One possibility is that she’ll never manage to significantly strengthen, despite all the favorable atmospheric and oceanic conditions, and thus will come ashore as a tropical storm. This would be in line with Dolly’s “personality.” The Houston Chronicle‘s Eric Berger mentions this as well:

I’ve been discussing the system for a week now, and it has long appeared to have the potential for significant strengthening. But it never really has. It’s possible, then, that Dolly will remain a tropical storm and not develop further. Given the storm’s history that might even be my bet.

“At the same time, however,” Berger adds, “conditions remain ripe for strengthening. And Dolly should get its act together over the Gulf of Mexico.” But how much so? That depends on a lot of things, including Dolly’s forward speed, which is currently quite fast, but is expected to slow down. The NHC writes:

ALL OF THE INTENSITY MODELS FORECAST AN UPWARD INTENSITY TREND UNTIL FINAL LANDFALL…BUT THEY DO NOT AGREE ON THE AMOUNT OF STRENGTHENING. THE SHIPS AND LGEM MODELS FORECAST ABOUT [75 MPH] IN 48 HOURS…WHILE THE GFDL IS A LITTLE HIGHER AT [85-90 MPH]. SINCE THE ENVIRONMENT APPEARS SO CONDUCIVE FOR STRENGTHENING…THE OFFICIAL FORECAST AGAIN LEANS TOWARD THE HIGHER GFDL SOLUTION. ANOTHER COMPLICATION IN THE INTENSITY FORECAST IS NOT KNOWING EXACTLY HOW FAST DOLLY WILL REACH THE COAST. IF IT MAKES LANDFALL SOONER THAN THE OFFICIAL TRACK INDICATES…IT MIGHT RUN OUT OF TIME TO REACH THE OFFICIAL FORECAST PEAK INTENSITY. BUT IF THE OPPOSITE OCCURS…DOLLY WOULD HAVE A LITTLE MORE TIME OVER THE WARM WATERS.

For his part, Alan Sullivan writes that “as the hours pass it seems more probable Dolly will not exceed category 1.” (Category 2 begins at 96 mph.)

Where will Dolly go? That, too, is a difficult question to definitively answer, but there seems to be a growing consensus that she’ll head for the Texas-Mexico border. Eric Berger notes that, although the computer models show a “wide spread” of possibilities, the all-important “dynamical models” — the GFDL, HWRF, GFS, NOGAPS and UKMET — “are in remarkably good agreement” 48 hours before landfall:

They’re spread from about 20 miles south of the Texas-Mexico border to 20 miles north. This should give us fairly high confidence that the system will strike near the border.

This may not happen, of course. The system could slow unexpectedly, likely allowing it to strengthen as well as giving a high pressure system to Dolly’s north time to recede. If this scenario unfolds Dolly could strike further up the Texas coast, possibly as far north as Corpus Christi.

I’d bet on the border, however.

The timing of landfall is also difficult to predict, even at this late date. Berger mentions the possibility that Dolly “could slow unexpectedly” — or rather, slow even more than what is currently expected. The NHC alludes to the opposite concern: what if Dolly fails to slow at all?

DOLLY CONTINUES TO MOVE QUICKLY [AT 18 MPH] . . . WHILE IT IS A LITTLE UNNERVING TO OBSERVE THIS FAST MOTION AND FORECAST THE CENTER OF DOLLY TO TAKE A COUPLE OF DAYS TO REACH THE COAST…ALL OF THE DYNAMICAL MODELS INSIST THAT THE FORWARD SPEED WILL BE ABOUT HALF ITS CURRENT VALUE BY TOMORROW NIGHT. THE MODELS AGREE SURPRISINGLY WELL ON THE SLOW-DOWN.

The current official forecast track has Dolly making landfall early Wednesday afternoon. If she continues moving at 18 mph, however, she’d arrive late tomorrow afternoon instead. That seems unlikely, since the models are in good agreement about the slowdown, but it’s easy to see why forecasters are a bit unnerved.

Regardless, one thing is clear: the tropical storm and hurricane watches will need to be upgraded to warnings later tonight, probably at 11:00 PM EDT. So Texas residents from Port O’Connor southward should expect to be under Hurricane Warnings in a few hours.