As mentioned last night, Emily did indeed have an eyewall replacement cycle ahead of her. The drop-off in intensity, from 135mph/952mb to 105mph/970mb, was more than expected. Of course, leave it to this storm to return with a vengeance. After the eyewall replacement cycle completed earlier this afternoon, the pressure rapidly fell, now sitting at 956mb as of 10pm tonight. With only weak to moderate shear over the storm, a strong jet to its north to "exhaust" the storm, and very high heat content and SSTs undernear the system, further intensification is likely and the storm may make a run at category 4 status once again.
Update: as of the 11pm Friday advisory, Emily is a category 4 hurricane once again. But, as with before, this may be a short-lived event. The latest recon flights have reported an open 10mi. diameter eyewall on the south & southeast sides of the storm along with a secondary wind maximum at a radius of 50mi., the first hints of another eyewall beginning to form and an eyewall replacement cycle to come. These fluctuations are expected with the storm, but pretty hard to predict. Once a day seems about commonplace, but can vary given the conditions around and within the storm.
During this reorganization phase, Emily once again has taken a stair-step towards the north, taking it on a path that would bring it precariously close to Jamaica sometime on Saturday. Upper-level steering winds are generally towards the west, but given the intensity of the storm and retrograding upper-low over S. Florida to its northwest, a slightly north of west-northwest path is likely in the shortterm, evening back out as the system nears Jamaica. In any case, it will be a close call for the island, and we can only hope that it spares them with a Charley/Ivan-like jog towards the west as it nears them.
Good news for one location, however, may spell bad news for another location. If the storm were to largely spare Jamaica, areas along the Yucutan Peninsula would likely see a more powerful storm. Most model guidance and the NHC official track currently call for the storm to pass near or over the tip of the Yucutan in 2-3 days' time; if so, this would spare the island from both the strongest part of the storm as well as the high wave action feared earlier this week. On its current path, however, it will likely pass just over the northern edge of the peninsula in about 2 and a half days.
Given inner-core fluctuations and the relatively small size of the circulation, a precise intensity is hard to pinpoint for that time; however, given what we have seen to date with the storm, somewhere in the category 3 range is a good bet, with the potential for both higher (given the high heat content of the NW Caribbean Sea) and lower (if shear increases instead of decreases) depending on the pattern evolution. Best call is for something in between at this time.
After that, the current NHC path towards the Mexico/Texas border and the Brownsville area looks good, although this may need to be adjusted slightly northward with time. A similar scenario to Dennis appears to be setting up with an upper-level low over S. Texas relatively cut-off from the main flow to the north.
How much this affects the ridge remains to be seen; however, it is further to the west than was seen with Dennis and does not appear to have to impetus to move towards the east or intensify to have a larger impact upon the track & intensity of the storm. Those from the Lake Charles, LA area and points south and west need to watch this storm in case its track begins to trend a bit further northward. The waters in the western Gulf are extremely warm, but upper-level conditions are forecast to grow increasingly unfavorable near landfall. After emerging off of the Yucutan, the storm should be in the middle end of category 2 strength, something it will likely hold to landfall.
While the storm should increase in size before that point, remember that relatively small storms can both intensify and weaken rather rapidly -- as we've seen in just the past 24hr -- making any intensity forecast problematic at this time, especially given the track uncertainty.
As for 99L -- there is a strong amount of shear currently over the storm, on the order of 30-40kt, leaving the center exposed well to the west of the area of deepest convection. This shear is in association with the same jet serving to ventilate Emily, for what it's worth. Were the shear to weaken, either in the vicinity of the storm or along its path as it moves west-northwest, it would have a chance to become better organized.
At this time, this does not appear as though it will be the case. It is still something to watch over the next few days, but Emily's still the only game in town. I'll have further updates as events warrant.
Sure are a lot of "if, ands, and buts" there.
Question, when/if you have a moment.......as one who folows these hurrican thread casually over the years, I don't believe I've seen the term "Eyewall replacement cycle" until this year. Does this represent some new thing into how the storms behave..a more cyclic nature of the ebb/flow of their ctrenght?