update on Hurricane Irma

Here is an update on Hurricane Irma – there is good news and there is bad news, but it is mostly bad news. This is a very serious storm and it’s going to take a lot of luck to avoid a major disaster in Florida. The odds now favor this storm joining Andrew, Camille, Katrina, Harvey and others among the most infamous hurricanes in American history. There is still time for luck to come out on our side, but there is precious little time left to prepare for a potential catastrophe.

 

Irma has weakened slightly, as expected, but the bad news is that it weakened from a near-record 185 mph sustained to a still-obscene 175 mph. (Pressure rose from 914 mb to 923 too.) Depending on the track we could drop all the way to 130-140 mph. That would be better than the alternative, but at that level we would still have a major catastrophe. The track will come into better focus (within a margin of error of 50 miles or so) by tomorrow night. The intensity is always tougher to pinpoint, but the overwhelming odds favor a major (Category 3 or higher, with sustained winds of 111-129 mph) making landfall on Saturday/Sunday. I think a Category 4 (130-156 mph) is more likely than Category 3.

 

The range of potential tracks is narrowing but still fairly wide, and there is room for Irma to miss Florida just off the coast (much as Matthew did last year). But this storm is huge, and there will be a path ~100 miles wide that experiences flooding and wind damage. A difference of just 20-30 miles could be the decider between devastation and moderate damage. There is still quite a bit of disagreement among the models down to the last 50-100 miles on Sunday morning, and that makes all the difference for the big population centers.

 

Here is a great time lapse of the official NHC cone/track projections. Notice the wobbles, which are important, but also notice how they track is broadly accurate over time. https://video.twimg.com/tweet_video/DJI-MJNV4AA0h4G.mp4

 

The bad news is that most tracks are zeroing in on south Florida, with Miami-Dade right in the bull’s-eye for some models. One experimental model puts a catastrophic Cat. 5 (906mb) landfall at Key Largo. (That would be the worst-case scenario, with the strongest winds and highest storm surge going right into Biscayne Bay and Homestead-Miami. I’d take the under on that wind/pressure, but as noted above it only helps so much.) One good model (ECMWF) just took the track back to the west by a few dozen miles, making landfall farther west in the Keys and SE of Marco Island before raking the entire Florida peninsula from north to south. That model puts hurricane-force winds through the entire state east of Tallahassee, and while it would be awful for the areas that suffer a direct hit it would be better for the major population centers.

 

Adjustments will have to be monitored right through the weekend. For now, the best-case of a total miss is <10% likely by my subjective compilation of the actual quantitative estimates. That leaves a 90% chance of a major hurricane landfall or near-landfall with hurricane-level damage in Florida. Events with a one-in-10 probability happen all the time, of course, but this is still very serious given the outcomes in the other nine cases.

 

I’d also put the odds at >50% for a direct hit in south Florida by a Category 3+ hurricane with severe damage and life-threatening conditions. I would split the difference in the direct-hit scenario, with about even odds between 90-120 mph winds in Miami and 140-150+ mph winds in Miami.

 

Again, the margin of error still exists, and there are no certainties. The extreme winds and surge could stay just offshore. But that is not the way to bet right now. Evacuation orders are up and they should be obeyed -- this is no time to play Russian roulette. And traffic already looks like a nightmare, so waiting until the last minute could be a problem.

 

A particular concern with Irma is the storm surge. Just as Harvey was a catastrophic wind producer over a small area but an even worse threat over a wide area from rainfall/flooding, Irma may do the same with its storm surge. See below for some NOAA simulations on storm surge from a Category 3 landfall at high tide.

 

The other bad news is that there is a growing likelihood that Irma will continue up the Florida peninsula – with significant damage all along the path – and possibly make a (second) landfall on the GA/SC/NC coast. One plausible – not assured, but plausible – scenario takes a strong hurricane into the Savannah/Hilton Head area. Another plausible scenario to the west takes 70-90 mph gusts all the way into Atlanta. But again, that is about four days away and important adjustments will have to be made. Other possible scenarios include a slow-wind down of the storm as it grinds north without a second landfall, in which case the damage in Georgia and South Carolina would be significant but more moderate. The bottom line is that everyone in the state of Florida east or south of Tallahassee and everyone on the east coast south of North Carolina should be paying attention to this storm.

 

 

 

Root for the American model. Unfortunately, the European model has been more accurate in recent years.

 

 

Other random notes:

 

• There has not been a Category 5 landfall in the U.S. since Andrew in 1992. (Hopefully Irma will be *only a Category 3 or Category 4 at landfall. But Katrina was a 3, Harvey was a 4, etc.)
  • Irma is roughly twice as big as Andrew. (The size and intensity at landfall are what matter, of course, and we’ll see. But Irma has already achieved higher winds than Andrew ever did, and its current hurricane-force windfield is ~100 miles across verus. 50-60 miles for Andrew. See below for images in a similar position that are roughly to scale).
• Coastal flooding is going to be a major problem. Low-lying areas and/or anything within close proximity of the beach is going to be major flooding. The storm surge forecast is 5-10 feet from Palm Beach to Miami to the Keys to Naples, and that is not likely to be wrong on the high side.
• Construction cranes in Miami pose a special threat because they are engineered to withstand 145 mph winds. Gusts could easily exceed that in the direct-hit scenario and there is no way to secure them in advance.

• Irma had a measured sustained wind of 185 mph for 37 hours straight – that is the all-time record for the planet in the satellite era (back to 1967, with caveats). It is normally not possible for anything but a Super Typhoon in the west Pacific to sustain 175+ for more than a 6-12 hour period.
• Irma is tied for second place in the Atlantic with 185 mph sustained winds. Only Allen in 1990 had officially sustained winds of 190 mph.
• The landfall Irma just made in the leeward islands is tied for second place all-time on the planet for sustained winds at 185 mph. Only three Super Typhoons in the Philippines and Taiwan were stronger at 190 mph (a rounding/measurement error, really). In this hemisphere no storm has ever hit land with stronger sustained winds; the Great Labor Day Hurricane that hit Florida in 1935 is officially credited with 185 mph sustained winds, but that is obviously speculative at best. The next closest would be a trio of storms at 175 mph, including Camille in 1969.
• The devastation in the Caribbean is extreme and the pictures are stunning. Loss rates – the number insurers use to calculate the share of buildings that will require substantial or total repair – are in the 30-90% range across several islands.  The human tragedy is just beginning to come into focus.
• Wind speeds were apparently strong enough on Barbuda to snap cell towers made of reinforced steel.
• Hurricane Jose is roaming the Atlantic behind Irma, and it could impact some of the islands recently hit by Irma. For now the long-range track for Jose looks to be out into the open Atlantic. The tracks and atmospheric dynamics of both Jose and Katia could also play a role in Irma’s ultimate track.
• By coincidence, exactly seven years ago there were three hurricanes (Igor, Julia, and Karl) in almost the exact same locations as Irma, Jose, and Katia today.

 

 

Here is one simulated IR satellite snapshot for Saturday morning. If that is even close to accurate – it’s far from infallible but it’s very likely close to accurate – it should send a chill down the spine of everyone in Florida.

 

 

 

 

NWS Miami is not messing around – nor should they.

 

Andrew:

 

 

Irma:

 

 

 

 

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