Hurricane Earl has been behaving like a well developed hurricane as during the day on Tuesday it has been going through an eyewall replacement cycle. Typically, the old eyewall collapses and a new eyewall forms. During this time, any given storm’s maximum winds will typically decrease in response to a rise in the central pressure. However, the energy tends to get dispersed throughout the storm, thus winds in the extremities may be higher than normally expected as the gradient is not quite as steep. This is what happened with Hurricane Katrina: it was going through an eyewall replacement cycle when it made landfall and so it was only a category 3 hurricane but, winds in excess of 100 mph were experienced well away from the center. I believe that the winds were about 125 mph at the point of landfall in Western Mississippi but winds of 108 mph were felt near Mobile Alabama. In any event, Earl should complete this cycle by Tuesday afternoon and thereafter some moderate strengthing is possible, though most models do not take it to category 5 status. So, it may max out at around 140 mph and not 155. What’s 15 mph amongst friends? It’s still an extremely formidable storm.
We had a big high pressure ridge over the Eastern United States last week and another ridge in the Atlantic with a trof in between. Hurricane Danielle followed the trof that split the two ridges and stayed well out in the open waters of the Atlantic. By this weekend, that weakness between the two ridges filled in and formed generally one large ridge from the mid Atlantic to the Eastern US with a slight weakness in the ridge along the US East Coast. Now, as hurricanes traverse farther north from the equator, the coriolis parameters become greater. The coriolis force is the apparent motion caused by the rotation of the earth. Any hurricane in the Northern Hemisphere will want to move to the right due to the rotation of the earth. Until the last day or so, the ridge to the north was strong enough to for the most part overcome the coriolis parameters and keep Earl moving generally westward. However, as Earl moved north of the Virgin Islands, it began to get toward the edge of the strongest part of the ridge and now is moving to the right of a westward track. Midday Monday it had a vector of 285 degrees and by the evening it was running at 300 degrees. This however is not the expected turn north.
That turn north will not occur until a trof moving across the northern part of the United States moves eastward to the US East Coast. When it does, it will provide the channel for Earl to turn north and run up the trof. A c0uple of things will happen at that time. The southwesterly flow ahead of the trof will pick up the storm and turn it north and then eventually north-northeast and then northeast and the forward speed of Earl will also increase. By the time its up to about 35 degrees North Latitude, it will most likely be scooting along at about 30 mph. That southwesterly flow will not only turn it and increase its forward speed, it should also disrupt the outflow aloft and that would tend to limit any intensification potential or even lead to a decrease in intensity. Even though there is a high probability of that coming about, it will still be a very strong storm with a high storm surge potential and its even possible that the forward speed might enhance the surge potential in the front right quadrant.
With regard to the intensity there is another potential fly in the ointment that could prove beneficial. I noticed yesterday a huge area of dry air on the water vapor imagery to the north of Earl. That dry air is not quite as large in scale today but it’s still there and is moving south. Earl will be moving right into that environment and I think that there is a fair chance that Earl may have some of that dry air wrap into it. If that happens, then the dry air will tend to weaken the storm. Hurricane Opal got a shot of dry air and it actually acted as a steroid shot for a few hours and the intensity jumped unexpectedly but then it fell quickly when that dry air got into the core. I believe that there is a chance that some dry air intrusion may take place. If so , that would be good news. Nevertheless, I believe the big story with Earl will be the ultimate track.
The spaghetti models have been consistently keeping the storm off the coast, though some recent runs had a model or two taking the storm inland in Maine or one even had it going in farther south in New England. The National Hurricane Center has been inching the official forecast ever so slightly westward for each of the most recent forecast tracks and has been pretty consistent in keep their forecast track to the left of the model consensus track. No one can say for certain at this point because it comes down to a matter of hours in regard to the trof digging into the East Coast. 6 hours difference in the timing would result in the difference of a major hurricane running right along the coast or running up say 80 miles offshore. While both scenarios would bring significant effects to the East Coast, a storm running just off the coast would be probably the worst case scenario. In that worst case scenario in my mind, the eye of the hurricane would remain over water so the intensity would not drop all that quickly. Meantime, coastal residents from North Carolina to Maine would feel the effects of a major hurricane, storm surge, winds and all.
There remain many scenarios as there are still several days for this to play out. However, I think its safe to say that residents of the Eastern Seaboard will feel the effects of a hurricane by the end of the week. The question is how much of an effect and no one can say with certainty what the answer to that question is. However, places like the outerbanks of North Carolina, the Virginia Coast, Long Island and Cape Cod will get the worst of whatever Earl has to offer. The history of hurricanes running up the East Coast is filled with examples of storms that weren’t too terrible, but there are also some glaring examples of storms that brought extreme devastation and loss of life. While we can’t avoid any devastation, there is no reason for loss of life as the potential is great enough with this storm for everyone to know that the better part of valor is to get out of the way. Remember, estimates suggest that a hurricane at its peak can release 10 to the power of 15 watts of total energy which equates to about 500,000 Hiroshima-type atomic bombs every day. Hurricane Earl quite literally is the most powerful force on the face of the earth right now and that is a battle man cannot win.
WTNT42 KNHC 312043 TCDAT2 HURRICANE EARL DISCUSSION NUMBER 26 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL072010 500 PM AST TUE AUG 31 2010 ALTHOUGH THE SATELLITE PRESENTATION IS NOT AS IMPRESSIVE AS IT WAS EARLIER...A RECONNAISSANCE PLANE AROUND 1700 UTC REPORTED A MINIMUM PRESSURE OF 940 MB AND MAXIMUM FLIGHT-LEVEL WINDS OF 128 KNOTS. THESE DATA SUPPORT AN INITIAL INTENSITY OF 115 KNOTS. CURRENTLY...THERE IS SOME SOUTHWESTERLY SHEAR DISRUPTING THE UPPER-LEVEL OUTFLOW OVER THE WESTERN SEMICIRCLE OF EARL. THIS SHEAR IS CAUSED BY A WEAK UPPER-LOW OR TROUGH OVER THE EASTERN BAHAMAS AS OBSERVED ON WATER VAPOR IMAGES. HOWEVER...MODELS WEAKEN THE UPPER LOW AS EARL MOVES AROUND IT...RESULTING IN A MORE FAVORABLE ENVIRONMENT. EARL IS EXPECTED TO MAINTAIN ITS CATEGORY FOUR INTENSITY FOR THE NEXT DAY OR TWO. EARL HAS BEGUN TO MOVE TOWARD THE NORTHWEST OR 305 DEGREES AT 12 OR 13 KNOTS DURING THE PAST FEW HOURS. THE SUBTROPICAL HIGH THAT IS STEERING EARL TOWARD THE WEST-NORTHWEST OR NORTHWEST IS FORECAST TO GRADUALLY SHIFT EASTWARD AS A BROAD TROUGH BECOMES ESTABLISHED OVER THE EASTERN UNITED STATES. THIS PATTERN WILL FORCE EARL ON A MORE NORTHWESTERLY AND NORTHERLY TRACK FOR THE NEXT DAY OR TWO. THEREAFTER...EARL WILL REACH THE BASE OF THE MID-LATITUDE WESTERLIES AND WILL LIKELY TURN SHARPLY TO THE NORTHEAST WITH AN INCREASE IN FORWARD SPEED. THIS IS THE SOLUTION UNANIMOUSLY PROVIDED BY TRACK GUIDANCE. ONCE AGAIN THE OFFICIAL FORECAST HAS BEEN SHIFTED A FEW MILES TO THE WEST BEFORE 48 HOURS FOLLOWING THE TRENDS OF THE ECMWF AND THE GFS. GIVEN THE LARGE AREA OF TROPICAL STORM FORCE WINDS ASSOCIATED WITH EARL...AND THE NEW DEFINITION OF WATCHES AND WARNINGS...A HURRICANE AND TROPICAL STORM WATCH HAS BEEN ISSUED FOR A PORTION OF THE MID- ATLANTIC COAST. INTERESTS FROM VIRGINIA NORTHWARD TO NEW ENGLAND SHOULD MONITOR THE PROGRESS OF EARL. FORECAST POSITIONS AND MAX WINDS INITIAL 31/2100Z 22.0N 68.8W 115 KT 12HR VT 01/0600Z 23.3N 70.5W 115 KT 24HR VT 01/1800Z 25.6N 72.8W 115 KT 36HR VT 02/0600Z 28.0N 74.5W 115 KT 48HR VT 02/1800Z 31.0N 75.5W 115 KT 72HR VT 03/1800Z 36.0N 73.5W 95 KT 96HR VT 04/1800Z 44.0N 65.0W 75 KT 120HR VT 05/1800Z 56.0N 55.0W 50 KT...POST-TROP/EXTRATROP $$ FORECASTER AVILA