Irene's potential landfall on the U.S. mainland remains several days away. So, let me be clear, my headline is based on the best estimate from the current guidance. There are a couple of decent weather models suggesting a track to Florida. There is also even one model (the Navy's NOGAPS model) that keeps Irene offshore completely. So, folks in Florida and even the extreme eastern Gulf need to stay on guard, and there is an outside chance that Irene may curve hard enough to stay out to sea - especially given her recent penchant for running a little north and east of the forecast tracks.
But at this point, the entire East Coast needs to be on alert. This even includes NY/New England. While the troughs (think: cold fronts... not 100% accurate, but close enough) are not what you'd expect to bring a New England hurricane (it usually requires a strong, sharp trough), the shape of the Atlantic ridge sufficiently does the trick. In fact, three models this morning show Irene striking NY/New England as a hurricane.
I'm not emphasizing NY/New England because that's where I think she's headed. It was more to make a point. We haven't discussed the Northeast much because the focus had previously been on the Southeast (and, note, a Northeast landfall does not preclude a Southeast landfall... Irene could hit NC, or even northern SC then head NNE, re-emerge over water near the Virginia Capes, then head up to NY/New England).
At any rate, stepping back to current conditions... Mother Nature giveth and Mother Nature taketh away, apparently. Irene has again nudged north of the forecast. This is great news for Hispaniola. The south side of Irene is the weakest. Don't get me wrong, the island will still be inundated with some pretty heavy rains - enough to cause some flooding and mudslides. But the problems could've been collosal if Irene tracked down the spine of the island. Now, they'll get spared the worst, as Irene stays offshore or, perhaps, just clips the NE coast of the Dominican Republic.
But what's good for Hispaniola is bad for those down the line (Bahamas and U.S.). Why? Well, most of you know that storms weaken over land. That's because they get their energy from the heat flux from the ocean. But further, unlike "regular" storms, hurricanes build themselves from the bottom up. So, the mountainous terrain of Hispaniola can really disrupt the storm badly. Now, however, it looks like Irene will just graze Hispaniola's northern coast. That means she'll probably only get disrupted slightly passing by the island.
Here's what Irene looks like now:
She is officially classified as a Category 1 hurricane now, though, so far Air Force reconnaissance data suggests that Irene may still be a tropical storm, just below hurricane status. No matter... it's very close to hurricane strength and has clearly intensified in the last 12-24 hours. So, if Irene isn't truly a hurricane yet, she will be soon. The latest recon fix center's Irene at 18.9N 67.0W. Check that out on the image above (tough to see the latitude/longitude lines, I know... but if you look at the bright red blob northeast of Puerto Rico, the center of Irene is near the southeast edge of that). Consider this: Irene was near St. Croix last night (that's the Virgin Island southwest of Puerto Rico). Point is, she's moved well north of west - more so than expected. If she resumes the previously anticipated motion Irene still may not quite miss Hispaniola, cutting across its northeast coast. But any continued northward nudging and she'll totally miss the island.
At that point, Irene will obviously miss Cuba and the question is, where does she go from there. We'll here's what the various models show:
...though there remain a couple of stubbornly far west solutions - the GFDL and UKMET - but there is a clear focus on the Carolinas. And notice the shift from yesterday. If you didn't see yesterday's forecast the biggest cluster was still in the Carolinas then, but was centered clearly on South Carolina. Today we've got an equal focus on North Carolina. This is a bigger deal than it may seem. A NC landfall opens the door for Irene to slip back off the coast near Norfolk, VA and continue NNE to a second landfall on Long Island and/or New England. Such a scenario is seen on the European model:
...and the American (GFS) model:
Side note on that European map, it doesn't show the storm near Long Island at that time step and it's long oast by the next step. What's not available to the general public, but I see from a different site (and, contractually, unfortunately, cannot share here) is an intermediate time step.
And if you think the crossing of land in NC and the cooler waters south of New England should kiil Irene sufficiently, think again. There is some clear weakening evident on the Euro, but it still has Irene near 950mb approaching Montauk Point, Long Island, NY, while the GFS has her at 973mb off the northern NJ coast. If those numbers are gibberish to you, that's fine. Doing a simple translation off of the Dvorak chart, those two pressures should correspond to a high-end Category 3 or a borderline Category 1/2 hurricane. So, a pretty sizable difference between the two, but clearly a hurricane at landfall.
Of course, NY/New England is secondary to the initial landfall, which could be anywhere from Florida to North Carolina. And if Irene could possibly be a Cat 3 (according to the Euro) when it reaches New England, then we really need to be concerned about that first landfall. Indeed, here's what the guidance shows on that:
...that's pretty impressive. Everything is over hurricane strength, with the best of them all indicating a Category 3 or 4 peak (and two of those drop off at the end only because of their probably-too-far-west track, with landfall over Florida inducing the weakening). So, Category 3 at landfall seems most likely based on this guidance. I wouldn't totally write off a slightly weaker landfall intensity - say, Cat 2 - as even the over-water HWRF shows Irene pulling back at the end (and the HWRF is notoriously too high with intensities).
The bottom line with all of this is that Irene should graze northern Hispaniola later today/tonight. Her intensity when she comes back offshore (if she moves over land at all) is hard to assess, as it depends how far inland into the Dominican Republic her center pushes and for how long. But since she should only scrape along the coast, I'd assume her inner core circulation will not be disrupted. As such, she should be able to rebound and then continue intensifying as she slows down and makes a slow curve through the Bahamas. As she makes the turn Irene could get dangerously close to Florida (not clear how close yet). Irene should then continue intensifying as she heads north towards the Carolinas. Given the trending, I'm favoring more of a NC landfall now, rather than a SC landfall. But it's way, way, WAY too early to try to narrow it down that much... just an early educated guess. But if I'm correct, this may also open the door for NY/New England. In short, this looks likely to be a significant event for the East Coast, even if we can't really nail down details. So, please stay on top of the situation if you live in or have any interests (family, friends, etc) on the East Coast. And check out my buddy "weatherdude" on here... he does a great job pulling together online preparedness resources.