Category 4 Earl Approaches the East Coast

Hi, Dr. Rob Carver with your evening blog update. It's a busy night in the tropics with category 4 Hurricane Earl and Tropical Storms Fiona and Gaston in the Atlantic. We'll focus on Earl tonight.

Earl
As of 11PM EDT, Earl is a Category 4 storm with sustained winds of 140 mph and faster gusts. From the advisory, Earl is located at 27.8 N, 73.8 W, 520 miles south-southeast of Cape Hatteras, NC. On average, Earl is currently moving north-northwest at 18 mph. Data from hurricane hunter flights show that Earl's pressure has fallen, the minimum central pressure is now 932 mb. Looking at Figure 1, an estimate of rainfall rates (think radar in space), we see a complete eyewall, with an especiallly vigorous thunderstorm cluster in the northwest quadrant. These


Fig. 1 Estimated rainfall-rate of Earl taken at 9PM EDT 1 September 2010. Image courtesy of the Naval Research Lab

Earl is still a large storm. Hurricane force winds extend 90 miles from the storm center and tropical storm force winds can be found 230 miles away. 12 foot seas extend at least 210 nmi from the center in all directions and may reach out to 450 nmi in the northeast quadrant of the storm. The most recent estimate (930PM EDT) of Earl's integrated kinetic energy is 91 TJ, with a wind impact of 3.1 out of 6 and a storm surge impact of 4.7 out of 6. Like Dr. Masters said earlier today, if the right front quadrant of Earl stays out to sea, the storm surge may not be as significant as this rating indicates.

Track Forecast
NHC has not really altered their track forecast for this update. Thanks to the subtropical high, Earl will continue turning toward the north as it moves around the subtropical high. When the trough in the jet stream comes out on Thursday, Earl will accelerate quickly to the northeast. The timing of the trough's arrival will determine Earl's impact on the East Coast. If the trough comes out quickly, Earl will stay at sea. If the trough is late in arriving, it could move Earl across the East Coast.

That said, the current forecast still holds that Earl's center will stay out to sea, but with Earl's center passing near the Outer Banks late Thursday night, then passing the Delmarva peninsula Friday morning before flying past Cape Cod Friday night and crossing over Canada's Nova Scotia Saturday. There is also a small possibility (less than 10%) that Earl could pass directly over the Outer Banks and/or the Delmarva peninsula. However, with a storm of Earl's size, the center does not have to pass overhead to cause damage. Please keep this in mind when considering your hurricane preparations.

Winds Forecast
Earl's size and track will produce tropical-storm force winds somewhere along the East Coast this weekend, and there is a 28% chance of hurricane-force winds along the Outer Banks. NHC puts out a very useful wind probability forecast. The highlights are that Cape Hatteras, NC has a 28% chance of hurricane-force winds and a 91% chance of tropical-storm (TS) force winds. A wide swath of 30+% probabilities covers the East Coast from Virginia to New England. Cities with a greater than 40% chance of TS winds include Norfolk, Ocean City, Providence, Boston, and Nantucket. Halifax, Nova Scotia in Canada has a 62% chance of TS force winds.

Earl is expected to maintain its current intensity until it meets the trough and starts moving northeastwards. The shear from the trough will start weakening it. It will likely go by Cape Cod as a fast-moving category 2 hurricane. When it goes over Nova Scotia, it will likely still be a tropical storm.
Current Watches and Warnings

Hurricane warnings are valid for the coast from Bogue Inlet, NC to the NC/VA border. Hurricane watches in effect from the NC/VA border to Cape Henlopen, DE and from Woods Hole, MA to Sagamore Beach, MA. Tropical storm warnings and watches cover much of the coast in between the NC/VA border and Woods Hole, MA. For the latest information on watches and warnings for Earl, visit our Tropical Alerts page.

Impacts
The primary threats from Earl are going to be storm surge, surf, and wind. Since Earl is forecast to gain speed after meeting the trough, flooding from rain should not be a large problem. From a broad perspective, storm surges are expected to be 3-5 feet above the tidal level, with large breaking waves at the coast. Beach erosion along the Delmarva peninsula and Outer Banks (8-10 foot breaking waves) could be significant. For more localized info, check out NWS's Hurricane Local Statements or our severe weather page.

What to do
People living in areas covered by the watches and warnings should be working through their hurricane preparation plans now. You have less than 24 hours to complete your preparations if you are in the Outer Banks and less than 48 hours in New England. Be sure to listen to local media for statements from emergency management agencies and the local NWS.

Fiona
All watches and warnings for Fiona were discontinued by the 5:00 PM EDT forecast. Fiona is forecast to curve northward without affecting land and dissipate in 4 days.

Gaston
Once Earl moves past Nova Scotia, this is the storm to watch in the tropical Atlantic. While it is far out at sea (more than 6 days to affect land), some computer models suggest Gaston could affect the Bahamas or the Caribbean. Statistical intensity forecast models (LGEM and SHIPS) rapidly intensify Gaston, but the dynamical models (HWRF, GFDL) do not. This storm will be worth watching over the next week or so.

Aerial Reconnaissance
The skies around Earl are going to be very busy Thursday according to the Tropical Cyclone Plan of the Day. There will be 3 flights from the Hurricane Hunters. NCAR and NOAA's Gulfstream's will be flying around Earl. HRD's WP-3D's will be flying research missions every 12 hours. NASA is sending several aircchraft as part of their Genesis and Rapid Intensification Processes (GRIP) mission. Their Global Hawk UAV will be flying for at least 24 hours. NASA's DC-8 has a six-hour mission scheduled. Finally, a WB-57 (one of the planes I supported during 2001's CRYSTAL-FACE) will also be flying high above Earl with microwave remote sensing gear. NASA has a nice list of the airborne instruments.


Fig. 2 Photo of Earl's eyewall taken from NASA's DC-8 Image Credit: NASA/Jane Peterson. (Full size image)

Next update
Dr. Jeff Masters will have an update Thursday morning. Dr. Masters, myself, Shaun Tanner, and myself will be participating in a special Hurricane Haven Thursday afternoon to discuss Earl's imminent approach. Dr. Masters will have the finalized details in his blog update.