Current position [18.5 N / 45.9 W]
First thing first. there is still A LOT of variation that can occur 7 days out! So this briefing isn’t to serve as a forecast, but as an explanation as to the components in play.
For the last few days, we’ve been waiting to see how far S and W Irma’s trajectory would dip. Like a ball that must bounce downwards before it bounces upwards, we’ve been closely watching the expected S and W dip that Irma is undergoing this weekend. The system is expected to begin it’s more northward trajectory on Mon/Tue, and therefore a narrowing of potential outcomes will only begin then. And no that doesn’t mean the final answer will appear, but a better picture will be revealed.
Now that WSW motion is indeed in place, but it initiated slightly higher north than previously modeled. A hurricane’s position is a result of the eye location, and to put it plainly, Irma’s been acting pretty shifty-eyed. The reason for this is the multiple occurrences of EWRC [eye-wall replacement cycles]: This is when a larger eye forms around an established eye. The larger eye “chokes” off the necessary moisture and the inner eye collapses. This process does weaken or prohibits further intensification during the process, but it is usually followed by a re-strengthening once the process is complete. So if the location of the eye is slightly changing, then it stands to reason that the point of where we measure it’s S and W movement also shifts.
If you’re following the models, remember that one release does NOT indicate certainty. You’re looking for consistency from run-to-tun. The GFS (American model) comes out 4 times a day. The European model is released twice a day.
Now as mentioned prior, there are many variables that will affect the trajectory of this system: The position of a high pressure located N/NE of the system, an upper level low located to the NW of the system, high and low pressure placement over the U.S. 6-8 days from now, and Irma’s interaction with any landmasses along the way or regions of increased wind shear [how winds change with height].
Three major factors are behind Irma’s current intensity, with the first two working against:
1) Its location in a region of cooler SST’s [sea surface temperatures], but by only about 1-2 degrees cooler than what’s consider tropical fuel.
2) Drier air ahead of the system is slightly wrapping into the inner regions, which dampens cloud/thunderstorm development.
But in the ‘ole gal’s favor is that its in a region of
3) Weaker vertical wind shear of about [10-15 kts] is a hurricane’s dream, as it does not destroy the thunderstorms from building vertically but still provides enough shift to keep the circulation in place.
But….Irma is moving into a region of higher SST’s (pro), moister (pro) air, and higher shear (con).
Considering all involved, further intensification is likely.
OUTCOME: For those in the U.S, take a deep breath, and consider tightening up your hurricane plans, because come next week, the time will come to either 1) pull the trigger or 2) exhale and consider yourself to have conquered yet another week during the 2017 Atlantic Hurricane Season.
But if you’re asking, “What would YOU do”, well, on this end, supplies are in place; because why not. Because what better way to actually relax this labor day weekend than to know whatever happens next week, as the picture sharpens, things are in place now. [Think of people who waited until the last minute to find solar eclipse glasses; how well did that work out?]
So, stay tuned, stay aware, and DO NOT buy into the hype anytime over the next 2 days.
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