Norcross: Tropical Storm Laura has formed, but there’s still high uncertainty in forecast for South Florida

Aug. 21 satellite image of Tropical Storm Laura.

Tropical Storm Laura has been named. The system that was Tropical Depression Thirteen now has enough of a circulation and winds over 40 mph, so it gets a name.  It has our immediate attention, of course, because the National Hurricane Center forecast cone is aimed right at South Florida. The system is forecast to impact the peninsula on Monday. The question is, what kind of storm will it be when that happens? It’s still a big open question.

But, while we should be wary about letting down our guard, the trend is good. 

Tropical Depression Fourteen is also a threat to land, though this system is forecast to head to Texas or Louisiana. Its future intensity is also a big question mark with lots of moving parts.

And new Disturbance #3 just moved off the African continent.

Tropical Storm Laura

Laura is still struggling against dry air and somewhat hostile upper winds as it approaches the northeastern Caribbean islands.  It’s a good-sized area of disturbed weather with a poorly defined center of circulation. But it’s enough to meet the criteria to be a named storm.

Hurricane Hunters have been working hard to find the center so we can track it accurately, but Mother Nature doesn’t always cooperate, and sometimes the center jumps around.  We’ll have to be ready for that.

Until the center becomes clearly defined, it’s still possible that the location of the center may shift with the circulation eventually forming in a different part of the disturbance.  In situations like this, where a relatively small deviation in the track will make a big difference in the strength of the system a few days from now, the only meaningful forecast is to comprise among a wide range of possibilities, which means we can’t focus on the details of the forecast. There’s a good chance they will change.

The computer forecast models indicate that the upper-level winds will become conducive enough for the system to continue to slowly organize. Dry air will continue to be nearby, however, so no immediate rapid strengthening is expected when the system is near Puerto Rico and the northeastern Caribbean islands later today and tomorrow.

The open question is, how close to the large islands in the northern Caribbean will the center track over the weekend. A track over or near the large and mountainous Caribbean islands would almost certainly not allow the system to significantly develop, or the circulation would get shredded, so only a weak storm would move through the Bahamas on Sunday and pass South Florida Sunday night into Monday.

If, however, the center of a decently developed system can stay far enough north of the islands to take advantage of the supportive atmospheric environment, the system could arrive in the Bahamas and at the Florida peninsula as a significantly stronger storm than forecast.  This stronger scenario appears increasingly less likely, though still not impossible.

As of this morning, the trends are good. Tropical Storm Laura is still poorly organized, and a number of the most reliable computer models track the system close enough to the mountainous islands that the system can never get well established, in fact some disrupt the circulation completely.

We’re on a knife’s edge here, however. Until we clearly see that the center of circulation is not going to thrive in the conducive atmospheric environment, we have to be ready to take quick action in case the center reforms and a strong storm quickly develops.

After the system, in whatever shape it’s in, passes South Florida, it will have the opportunity to intensify in the Gulf of Mexico as its track bends north toward the northern Gulf coast. Things get complicated there because Thirteen’s intensity and track might be affected by whatever comes of what’s now Tropical Depression Fourteen.

Satellite of the tropics on Aug. 21, 2020.

Two strong storms cannot exist in the Gulf at the same time without deflecting each other. Though most often, one is stronger than the other, which allows it to dominate the space around it, further weakening the other system.

What the relative intensities of these systems will be when they arrive in the Gulf about Tuesday is not knowable at this point.

Tropical Depression Fourteen

The center location of Tropical Depression Fourteen is iffy as well.  Hurricane Hunters examined the system found a broad calm area well south of the presumed center of circulation, and now it appears there are multiple swirls vying to be the center.  This means that the forecast could still jump around to some degree as a tropical storm finally organizes.

If it weren’t for the fact that Fourteen will probably track over the corner of Nicaragua and Honduras, it would likely strengthen, perhaps significantly, before it gets to the Yucatan Peninsula of Mexico.  If it can somehow avoid the land, a stronger storm might well move into the Gulf. 

As it is, the land and the future proximity of Tropical Storm Laura or its remnants throw a monkey wrench in our ability to make a confident intensity forecast.

In any case, the computer forecast models are fairly well aligned with the idea that a storm of some sort will track toward the Texas or Louisiana coast early next week.

Tropical Depression Fourteen: 8 a.m. Friday advisory. (www.HurricaneIntel.com)

Tropical Disturbance #3

The large disturbance we have been tracking over the African continent has moved out over the east Atlantic. The disturbance is showing signs of circulation, and it will likely become a tropical depression or tropical storm in the next few days. 

Down the road, the atmospheric environment is forecast to deteriorate, however, which would tend to force the system to track to the west.  It will be another system to keep an eye on.


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