Intensity
As suggested by satellite last night, Earl has strengthened overnight. A recent recon pass showed that the central pressure was down to 929 mb, and showed 161 mph flight-level winds in the NE quadrant, which translates into surface winds of around 145 mph. This surface reading is supported by a dropsonde that in the northern eyewall (not quite the most powerful part) reported 136 mph surface winds, and by satellite intensity estimates that agree on an intensity of 125 kts (145 mph). Based on these numbers, I will be very surprised if the NHC does not raise the intensity to 145 mph at the upcoming 5 AM EDT advisory.
Again, though, it appears that the advisories will have missed the maximum intensity of Earl. By the time of these recon numbers, the hurricane’s appearance on satellite had noticeably deteriorated since a few hours ago, and the hurricane hunters reported that the eye was becoming elliptical, in contrast to the perfect circle just recently. Shortly after midnight EDT, satellite intensity estimates put Earl between 150 and 155 mph, just as they did at the end of its rapid intensification Monday night. But again, the NHC decided to err on the side of conservatism.
Despite this intensification, however, Earl’s IKE (storm surge category) had declined from 5.0 to 4.7 by 01:30 UT, and may have declined even further since. As is common with intensifying storms, Earl has become more tightly wound, and it appears now that hurricane-force winds extend no more than 80 miles from the center, not 100. If this trend holds, then the wave and surge potential may be reduced slightly. However, it is likely that this trend will not hold. I would expect Earl to begin an eyewall replacement cycle by the time it nears the NC coast, and eyewall replacement cycles are often accompanied by an increase in windfield, sometimes a permanent one. Isabel’s IKE did not peak, if I recall correctly, when she was a monster Cat. 5 annular hurricane, but when her eye had collapsed and she was a vastly extended Cat. 2.
Track
Now, what about track? Right now, it’s not looking good for the east coast, but it’s not looking terrible either. After Earl’s northward wobble yesterday evening, it has resumed a NW/NNW motion, and is pretty much right on track with the forecast points, or a little to the left. The key barometer right now is the 75/30 mark--75 degrees west, 30 degrees north. The official forecast track takes Earl pretty much right over this point, and so if Earl passes just to the east and north of the 75/30 mark, then it is east of the forecast track, and thus very likely to keep a safe distance from the coast. However, if Earl passes to the west and south of the 75/30 mark, then it is west of the forecast track, which means it is quite likely to bring hurricane-force winds to the NC and MA coasts, at least. If it goes west of the 75/30 mark and still delays to make the northward turn, passing 76 or 76.5 W, then odds increase rapidly that it will actually make a US landfall. Currently, Earl seems determined to past to the south and west of the 75/30 mark. As of the last recon fix, it was 74.5W and 28.75 N, and an extrapolation of its last 6 hours of motion would take it over the 75W mark at 29.4 N, and across 30N at 75.5W. Until Earl makes that northward turn, no one can breathe a sigh of relief.
Now let’s look a bit more at hurricane-force wind and landfall probabilities. In his recent Wunderblog post, Dr. Rob Carver reported that the NHC Wind Probability product gave the Outer Banks a 28% chance of hurricane-force winds, and Carver went on to give them only a 10% chance of an actual landfall. But once again, if I’m understanding the cone of uncertainty correctly, this doesn’t make sense. The western edge of the cone of uncertainty has Earl going over the Outer Banks, and remember that there is always a 16.7% chance of the hurricane missing the cone to the left. This means we are looking at a 20-25% chance of NC landfall. As for hurricane force-winds, these are expected, at the time of closest approach, to extend 60 mi northwest of the center. And, as the hurricane is currently forecast to miss Cape Hatteras by only 50 miles, this means that there is around a 55% chance of Hatteras getting hurricane-force winds, since any track to the left or slightly to the right of forecast would bring hurricane winds to the coast. Once Earl is showing signs of making his northward turn, I will post again with more landfall and hurricane wind probabilities for various points in the mid-Atlantic and northeast.
Waves and Surge Report
Buoys off the SE coast continue to report enormous waves being generated by Earl. Buoy 41047, which Earl passed around 75 miles west of last night, is currently reporting significant wave heights of 19.7 ft., down from a peak of 31.5 ft. (this marks 24 hours straight of 19-ft.-plus seas). Closer to the coast and further away, on the weaker west side of the storm, Buoy 41010‘s observations have recently peaked at 21 ft. To the north, near the SC and NC coasts, wave heights have not yet increased significantly, but will soon. One silver lining on this cloud is that Earl’s rapid motion (which will be increasing more and more over the coming day) will limit its wave generation, and means that the battering surge and waves on the coast will not last long--this is key for beach erosion, which is due more than anything to long, drawn-out batterings. Buoy 41046, over which Earl passed yesterday morning with 49-ft. significant wave heights, is now, 25 hrs. later, reporting “only” 13.1 ft. waves.
Tides are just now beginning to run above normal on the GA and SC coasts--only a foot above normal now, though that will certainly increase later on, and will be of course much worse in NC and VA. Later, I will post regarding locations that are likely to have high tide coincide with the closest approach of Earl.
BREAKING UPDATE: Recon has just reached the center of Earl once again, and shows a due northward movement over the past 2 hrs. This could mean that Earl has made the turn already, east of 75W, or it may be just another wobble. Only time will tell. Also, 5 AM EDT advisory has just come out, upping the intensity, as expected, to 145 mph, and significantly, altering the forecast so Earl is still a Cat. 4 when it makes its closest approach to NC. If Earl did in fact make landfall anywhere in NC as a Cat. 4, it would be the first hurricane to do so since Hazel in 1954.
