8/26/19 2AM update: Tropical Storm Dorian

As the overnight data continues to trickle in, not much has changed in the short term with Dorian.

But as we look toward the Labor Day weekend, the overall pattern is starting to look a bit clearer. That’s not to say that “we now know where Dorian will go!” but rather, “we have a better idea about the range of possibilities!”

Latest on Dorian

SUMMARY OF 200 AM AST…0600 UTC…INFORMATION
———————————————-
LOCATION…11.8N 55.8W
ABOUT 270 MI…430 KM ESE OF BARBADOS
ABOUT 375 MI…605 KM ESE OF ST. LUCIA
MAXIMUM SUSTAINED WINDS…50 MPH…85 KM/H
PRESENT MOVEMENT…W OR 280 DEGREES AT 14 MPH…22 KM/H
MINIMUM CENTRAL PRESSURE…1003 MB…29.62 INCHES

Dorian doesn’t look quite as healthy as of this writing on Infrared, but don’t let that fool you. The system is quite small, but don’t let that fool you, either. The max wind is within 10 miles of the center. According to Tropical Tidbits, the area of circulation is only 100 miles.

But the forecast is for the system to continue to intensify.

The National Hurricane Center forecast has Dorian moving through the Caribbean as a strong Tropical Storm or weak Hurricane.

At 200 AM AST (0600 UTC), the center of Tropical Storm Dorian was located near latitude 11.8 North, longitude 55.8 West. Dorian is moving toward the west near 14 mph (22 km/h). A turn toward the west-northwest is expected later today, with this motion continuing through Tuesday night. On the forecast track, the center of Dorian is expected to be near the Windward Islands late today and tonight and move into the eastern Caribbean Sea on Tuesday.

Maximum sustained winds are near 50 mph (85 km/h) with higher gusts. Strengthening is expected during the next few days, and Dorian could be near hurricane strength by Tuesday over the eastern Caribbean Sea.

Dorian is a compact tropical storm. Tropical-storm-force winds extend outward up to 45 miles (75 km) from the center.

The estimated minimum central pressure is 1003 mb (29.62 inches).

To the Data!

Like I mentioned initially, the overall pattern is clearing up a bit. Nothing is locked in (it never is with tropical systems) by any means, but there are some things we can start to pull out of the data.

A big piece of the eventual Dorian puzzle that everyone wants to know is, “What about where I live?”

That is tough to answer because the life cycle of Dorian is going to be complicated by a handful of factors.

1. Two passing upper-level areas of low pressure
2. mid-level wind shear
3. low- and mid-level dry air
4. Two competing ridges of high pressure

So, while we can’t figure that out – specifically – where Dorian will be in a week, we are starting to get a better idea about where the pieces of the puzzle that are going INTO figuring that out. You can see that in the above montage image of high pressure. One ridge slides west, and another builds in behind it as Dorian – or what is left of it – approaches the Bahamas.

But let’s back up a few days…

Both the ECMWF and the GFS computer weather models show Dorian moving west-northwest across Haiti and the Dominican Republic by Thursday. That lines up with the National Hurricane Center forecast, too.

After that point, forecast models have Dorian interacting with wind shear and two areas of upper-level low pressure. The storm will also be traversing an island with very high mountains that may help to rip the system apart, too.

So when we say “Dorian – or what is left of it” that is because there is a fair amount of evidence in the modeling that Dorian may struggle to maintain itself after Day Four (Thursday).

Because tropical systems move based on mid- and upper-level winds, and the effects of those winds on the track is dictated by the system’s strength, the forecast model guidance for track is thus… dictated on strength.

How strong will it be? That’s a great question.

According to model guidance… somewhere between a Tropical Depression and a CAtegory 3 Hurricane.

Some help, right?

And that can complicate things. Because when you see something floating around social media like this:

It can feel very scary.

But know that there are a lot – and we mean a lot! – or assumptions that the models are making to come up with that darker black line. And one big one is strength (also known as intensity).

And beyond five days, these models are rarely (if ever) accurate with specifics like that. But they are great with showing trends an generalities.

In general, model trends suggest that Dorian gets ripper apart moving from the Caribbean to the Bahamas. And from that point two ridges of high pressure set up, allowing an alleyway between 150 miles east of Jacksonville, Florida and about Houston, Texas for Dorian to travel north through.

That’s a big hole. And a lot of uncertainty.

Discussion of the data from the NHC

Dorian’s cloud pattern hasn’t changed much since this afternoon, with deep convection oscillating up and down. There are few banding features evident, and the upper-level outflow is somewhat restricted over the eastern semicircle of the circulation. The intensity estimate remains at 45 kt and is in agreement with a recent Dvorak estimate from TAFB. The intensity forecast for this storm is a challenge, since the numerical guidance depicts a wide range of possibilities. The GFS and ECMWF global models dissipate Dorian over the Caribbean in about 4 days, probably due to the hostile environment associated with an upper-level low near Hispaniola. Another unfavorable factor could be dry air that is also forecast by the global models over the Caribbean. On the other hand, the statistical/dynamical models DSHIPS and LGEM do not weaken the
system until it interacts with the land mass of Hispaniola. The official forecast is close to the intensity model consensus, IVCN, but it should be noted that there is greater than usual uncertainty associated with this forecast.

The motion continues to be slightly north of due west or 280/12. Dorian is moving along the southern side of the subtropical ridge. The track models are in good agreement that the cyclone will gradually turn toward the west-northwest on Monday. A slight weakness in the ridge near 70W longitude in a couple of days should induce a gradual turn to the northwest later in the forecast period. The official track forecast is close to the corrected consensus, HCCA prediction and is also very close to the previous NHC track.

I live along / near the Gulf Coast… So what’s the forecast for us right now?

There isn’t one specific to you. Stay alert to changes. Watch the forecasts. Stay tuned.

I wish I could offer more specifics, but that can’t be done yet. In general, those two ridges I just talked about are going to play a big role in where Dorian goes. But where it goes between those two ridges is going to be dictated by how strong it is when it leaves the Caribbean. And how strong it is when it leaves the Caribbean is going to depend on the track through the Caribbean as well as how it interacts with dry air, wind shear and two upper-level lows. And how it interacts with those three things is going ot be the track through the Atlantic toward the Windward Islands.

You can see how fast we get down a rabbit hole, here. Sadly, with Tropical systems, that is how it goes.

The good news is that we learn new stuff every day about the track, strength, and impacts. So staying tuned to the forecast daily is super important. And will be helpful – incrementally.

But you can’t just grab the forecast today, and make plans for what will happen a week from now. Sadly, that’s not how it works.

So what can we do now, Nick?

Check over your Hurricane Preparedness Kit. Do you have all of the necessary items? Food? Water? Medicine? Do you know if you live in an area that would need to evacuate? If not, what is your personal threshold for choosing to evacuate? If you don’t know, find a friend who has lived through a hurricane. Ask them!

And keep an eye on the forecast. Things will change daily. Prepare for that. Don’t just check the forecast once and think you’re good to go.

And, most importantly, if you’re someone who stresses over htings like this… take some time to work on relaxation. Uncertainty with a system like this can – I’m sure – raise anxiety a bit. But know that sometimes uncertainty is a good thing in meteorology. Because we don’t know for certain where it will go, means there is a good chance, that as of now, it isn’t headed toward you.

Could that change? Sure. But try to remember to cross that bridge when it gets here. For now, review your plan and your kit. That way you are prepare for whatever comes this way. Even if it nothing.