CajunWX — Berwick Bay Storms

Here is the Thursday update on the “little system that could,” good ole Invest 99L. If anything, the system looks worse than it did yesterday at this time. But there are some subtle signs things may be about to change. First off there is now a low-level closed circulation obvious on the visible satellite images.

If you look at the tip of the arrow, just north of Hispaniola, you can see the banding of the low-level circulation. Observations and hurricane hunter aircraft have found a 1008 mb central pressure with sustained winds of 35 knots and gusts to 45 knots. It has an overall circulation of 140 miles diameter and a maximum wind zone of 80 miles diameter. It is a healthy system, so why isn’t it named?

Because of what is missing from yesterday.  All those big thunderstorms surrounding the center are gone. Well not really gone, just displaced. They are well to the east and south of the system. So what’s up? Well the dry air is a gone, but that nasty shear zone we talked about yesterday is now directly over 99L and at its most intense. As you can see in the next image, a small lobe of highly intense negative wind shear is right over the center of the system.

The left arrow points to where the center is at the time of the image. Remember, it is the red lines which are unfavorable to development. Yellow indicates a favorable environment. It may be hard to see, but the right arrow points to a number “30” indicating that winds of 30 knots or greater are pushing all of the thunderstorms to the east and south. Add that 99L is chugging west-northwest at about 20 knots and that equals a true shear of over 50 knots. Few systems can take that kind of beating. But 99L is hanging in there. And most importantly, the shear models indicate the shear lobe will pull east as 99L moves west into an area with highly favorable conditions. Remember the red lines are unfavorable, but those green lines equal favorable conditions. There is lots of green just ahead of 99L!

The bottom line here is that the next 36 hours are critical. If the circulation is still there in 36 hours as the strong shear is replace by favorable conditions, we will likely be looking at Hermine and she will be poised to steadily intensify. My guess is that she will make it. Had the center been closer to Hispaniola, with its huge mountains, and not over 85 degree waters, I would say no way. But unless those shear models are wrong, I feel we have a tropical storm within 36 hours.

So what happens if Hermine is sitting in the Bahamas Friday afternoon or evening? Well the models have settled down a bit and have a better feel for the system. But there is some volatility still in their outputs. In some ways, the models are also influenced b y their peers. In the afternoon run of the ECMWF yesterday, the Euro actually shifted its tracks to a recurve over Florida. Why? Because of the erroneous output of the GFS model, it was accounting for something not truly there. When the latest run came out this morning, it was pretty much the same as we looked at yesterday.

It is a track that is perfect for intensifying a system. Again, ignore the actual individual lines and look at the cone of probability they project. Basically, they show a system moving through the southern Bahamas, then through the Florida Straits, and slowly bending west-northwest into the Gulf of Mexico. What is missing in that track? If you said it does not cross any major land mass, give yourself a gold star. If this track holds, the system will miss Hispaniola, stay north of Cuba and south of anything but maybe extreme southern Florida and the Keys. Land masses inhibit development and intensification, while most of the time actually disrupting systems. It would not be a good thing for Florida if it crossed the width of the state, but it would be a good thing for those of us along the northern Gulf Coast. It would slow development. That does not appear to be the case.

As for intensity, there is a bit of hope there. Most of the projections show a strong Cat I storm sitting due south of say Pensacola Tuesday heading toward the Louisiana Coastline somewhere. Giving that the trend is slow intensification and it is likely another day or so from landfall, we could interpolate a weak Cat II storm at landfall.

Again, all of this is a week out on a system which has yet to get its act together. That said the models seem to think it will come together and begin to slowly gain strength over the open waters of the far western Atlantic, Florida Straits, and Gulf of Mexico, all of which are a cauldron of pent up thermal energy just waiting on a system to come along. In addition, it is often easy today to get too caught up in models and projections, while ignoring that trait which separates good tropical meteorologists from the so-so one; their gut. In so  many ways, all weather forecasting is as much an art as science. The models are only as good as the data we put into them. Over the continental US, we have a high density of data points and our models do a pretty darn good job. They do a good job over the open waters as well but must do so with far less data. So the key is to step back and ask yourself, what would I have thought about this system 25 years ago before the supermodels? Most of the old guys out there like myself seem to think this system will make it. Over the past 10 days, it has run through some of the most adverse conditions you could imagine, yet we are still talking about it. I just have to believe that once it gets some good conditions, it is going to take off.

Again please do not focus exactly on those forecast paths. At five days they may be off by up to 300 miles either side of the centerline. But bottom line, if you live anywhere from Corpus Christi to Pensacola on the Northern Gulf Coast you need to be doing two things: First, keep an eye on then progress of the system and listen to what the NHC and NWS have to say. Second, begin very preliminary preparations for a possible threat from a tropical system in the middle of next week. Even if nothing come of 99L, you will have that done when the next threat appears and be better off for it!