Earl peaks, turns, and threatens to grow

Before I post the latest track forecast, it’s important to emphasize that Hurricane Earl is not a point on the map, but a broad storm system with a geographically large wind field. The exact course of the eye is important, especially for storm surge purposes, because the strongest winds and most damaging surge — especially when it reaches New England, by which point its forward speed will be accelerating, even as its rotational winds decrease — will be in the storm’s right-front quadrant. Thus, if the eye remains offshore, even by a few dozen miles, things will be much better than if the eye makes a direct hit, thus bringing that maximum surge onto the coastline immediately to the east of the landfall point. However, having said that, there will be plenty of rough weather on shore regardless of the storm’s exact track, because the wind field is large, and possibly about to get larger:

THERE HAS BEEN NO SIGNIFICANT CHANGES IN THE STRUCTURE OF EARL DURING THE PAST FEW HOURS. HOWEVER..MICROWAVE INAGERY SUGGEST THAT AN EYEWALL REPLACEMENT COULD OCCUR SOON…IN WHICH CASE THE WIND FIELD WOULD BECOME LARGER.

Earl very likely peaked in intensity at 140 145 mph as of 5am, and he’s now down to 140 mph, probably the beginning of a slow, steady weakening trend. The eyewall replacement cycle will kick off this trend, and by the time the cycle is complete and the storm would be ready to re-tighten again, shear will have increased further, and then the waters will get cooler. So Earl is officially on the decline. But no one ever expected this storm to make landfall as a Category 4, so that’s not too surprising. The potential widening of the wind field could be a bigger deal, increasing the storm’s impact in North Carolina and especially in New England and the Maritimes, since the eventual start of an extratropical transition as it accelerates north is likely to make that widened wind field even wider. This is going to a big storm — not catastrophic, but widely felt over a broad area.

Anyway, here’s the latest forecast track:

Watches and Warnings, as you can see, now stretch all the way from Cape Fear to Nova Scotia. (Red is Hurricane Warning, Pink is Hurricane Watch, Blue is Tropical Storm Warning, and Yellow is Tropical Storm Watch.) I’m not sure why the land on either side of the Bay of Fundy isn’t covered yet — I’m guessing they’ll be added in the next advisory. Timing of landfall will be very important there, as Fundy has the highest tides in the world, so a landfall at high tide would be quite something.

Earl is now officially moving due north (well, almost — 355 degrees), so the first part of its “turn” has happened on schedule. Next, it is expected to turn to the NNE in the wee hours of tomorrow morning, mere hours before making its closest approach to Hatteras. From its current position, if it were to keep moving at 355 degrees or so, give or take a wobble, it could make a direct hit on the Outer Banks. But that’s not expected to happen.

Watch for that turn to the NNE overnight tonight, in the hours before landfall. If it doesn’t happen, things will be much worse in North Carolina than we’re expecting, and although there’s no particular reason to believe the turn won’t happen — the computer models have handled this storm pretty well — it’ll be far too late to adjust preparations or evacuation plans if the forecasts turn out to be wrong. North Carolinians should be making final preparations to protect life and property now, and doing so on the basis of a direct hit tomorrow morning, even though that’s not the most likely scenario. If you’re in this storm’s path, batten down the hatches — or, if the local officials tell you to evacuate: Do it! Get the Hell out!

P.S. Dr. Jeff Masters has an excellent post rounding up the potential impacts, including:

Earl’s eye is expected to stay offshore of North Carolina. However, much of coastal North Carolina will experience tropical storm-force winds of 39+ mph for a period of 12 – 18 hours beginning this afternoon or early this evening. Earl’s expected radius of hurricane-force winds of 90 miles to the west may bring hurricane conditions to the Outer Banks, but probably not to mainland North Carolina. Earl’s radius of tropical storm-force winds to the west, over land, will probably be about 150 miles, so locations from Wilmington to Norfolk could see sustained winds of 40 mph. Storm surge will likely be less than two feet along the North Carolina coast west of Cape Hatteras facing the open ocean, since winds will be offshore. However, a significant storm surge of 3 – 5 feet can be expected on the south side of Pamlico Sound, due to strong northerly winds. A 3 – 5 foot storm surge is also likely along the Outer Banks from Cape Hatteras northward 50 miles to Nags Head. NHC is giving a 10% chance that the storm surge will reach 7 – 9 feet along the coast near Nags Head. It is possible that Coastal Highway 12 out of the Outer Banks will be blocked by sand and debris, or washed out, resulting in a multi-day period where everyone on the Outer Banks will be stranded. …

Residents in Eastern Long Island, Rhode Island, and Southeast Massachusetts need to complete all of their hurricane preparations by early Friday morning. By Friday afternoon, winds will rise quickly. Earl’s recent increase in strength means that New England will see a stronger hurricane than was expected. The latest track forecasts still keep the eye barely offshore, or have it passing over Nantucket and the extreme eastern tip of Cape Cod, Massachusetts. The 5am NHC intensity forecast calls for Earl to have top winds of 100 mph at 2am Saturday, when the storm is expected to be over or just offshore of the eastern tip of Cape Cod. Earl will be moving near 25 mph at that time, meaning that that top sustained winds on the north side of the eye, over land, will be 50 mph, and the winds will be 100 mph on the south side over water. NHC is giving a 10% chance that a storm surge of 3 – 5 feet will occur in Long Island Sound (Figure 4), and 2 – 3 feet along the south coast of Long Island. A small deviation in Earl’s track to the left, resulting in a direct hit on eastern Long Island and Providence, Rhode Island, would probably be a $10+ billion disaster, as the hurricane would hit a heavily populated area and drive a 7 – 15 foot storm surge up Buzzards Bay and Narragansett Bay. The odds of this occurring are around 3%, according to the latest NHC wind probability forecast. The forecast is calling for a 28% chance of hurricane-force winds on Nantucket, 7% in Providence, 4% in Boston, 7% in Eastport, Maine, and 17% in Hyannis. …

Winds will begin to rise on the southwest coast of Nova Scotia early Saturday morning, and all preparations need to be completed by Friday night. By late morning Saturday, Earl is expected to make landfall somewhere between the Maine/New Brunswick border and central Nova Scotia. At that time, Earl will probably be a Category 1 hurricane. Earl will be moving at a very rapid 25 – 30 mph when it arrives in Canada, and regions on the right side of the eye can expect winds 50 – 60 mph greater than on the left side, due to the fast forward motion of the hurricane. It is unlikely that Earl will be as damaging as Hurricane Juan, the 2003 Category 2 hurricane which made a direct hit on Halifax, Nova Scotia, causing over $200 million in damage. …

Regardless of Earl’s exact track, the U.S. East Coast can expect a long period of high waves today and Friday. Significant beach erosion and dangerous rip currents will be the rule, due to waves that will reach 10 – 15 feet in offshore waters. Waves are expected to reach 25 – 30 feet along the Cape Hatteras, North Carolina shore tonight. Beach erosion damage in the mid-Atlantic states will likely run into the millions[.]

[Cross-posted at Sullivan’s Travellers.]