MyFoxHurricane.com blog

Earl Closer to U.S./Third threat to Leewards

Posted by Andy Johnson under Daily updates

Hurricane Earl continues to look very impressive today in satellite images. Hurricane warnings were issued at 11AM EDT, September 2, 2010 for parts of North Carolina and could be extended northward over the next 36 hours to include parts of the mid-Atlantic States and New England. Hurricane watches were issued at 5PM Wednesday as far north as Massachusetts. If you have interests anywhere along the east coast from North Carolina to Nova Scotia, you should carefully follow the progress of this dangerous storm as he moves northward. Most of the models keep the center of strongest winds in Earl offshore. However, it is very important to remember than just a small change in direction could mean a major change in impact. Forecasting storms that are parallelling the coast are more difficult storms that are hitting perpendicular to the coast. A change in heading of 10° in a hurricane paralleling the coast could mean a difference of landfall of hundreds of miles. A change in heading of 10° in a hurricane moving perpendicular to the coast might only mean a difference in landfall of 50 miles or so depending on where the initial position was.

The other issue unique to the east coast is that as Earl accelerates to the north or northeast on Thursday and Friday, the translational forward speed of the hurricane which is added to the rotational speed will become more of an effect. This means that winds on the east side of the hurricane will be more unevenly distributed and stronger than on the west side where the translational speed will be subtracted from the rotational speed. So, if the hurricane were to move inland in North Carolina or New England the area just to the right of the eye would experience much more damage than the area not too far to the west. If the eye remains offshore, there will be gusty winds, high surf and beach erosion but not catastrophic damage or flooding. Storm surge flooding could be a problem if the storm makes landfall, especially at high tide, but would not be as severe if the hurricane remains offshore. Huge waves will still pound the entire East Coast, however, regardless of whether or not the hurricane makes landfall.

Do not just follow the thin black line of the forecast track. Look at the yellow cone of uncertainty. If you are in the cone you are in danger of a strike.

The gaphics below show the probability of sustained tropical storm force winds and sustained hurricane force winds respectively.

I’ve plotted the Air Force Flight 306 on Skytower OMNI shown below. The vortex message on Wednesday, August 2 at 11:27 AM EDT, showed a maximum sustained surface wind of 101.3 MPH and a maximum flight level sustained wind of 126.6 MPH at an elevation of 8572 ft. The flight meteorologists reported a closed circular eye.

The high resolution McIDAS GOES E satellite image shown below clearly shows the circular eye as seen from 22,500 miles above the earth’s surface.  

The image below is a magnification of the McIDAS image below. Even though there are some low ragged clouds in the eye which prevent the observer from seeing the ocean surface, the eye seems to have a “stadium” effect with the edges sloping out with height. Transverse banding can be in chaotic eyewall indicating significant turbulence. An outer cloud top maximum rings the inner eyewall. Earl has been undergoing eyewall replacements over the last 2 days. It is possible that the outer ring could contract and form a new inner eyewall over the next 12 to 24 hours.

The high resolution GOES image of Fiona shown below confirms a circular appearance to the low level cumulus clouds. The IR images do not show the circulation, as well. Sometimes, the visible images can show features that are not as defined in the IR images. Radar data from the Leeward Islands also showed a circular appearance to the center which was not evident in some of the infra-red images.

Even though the early run of the GFS model did not pick up on the development of T.D. #9, we have been watching the tropical wave since it emerged off of Africa. T.D. #9 was upgraded to Tropical Storm Gaston at 5PM Wednesday. Yet, another strong wave is about to emerge, as well. The next name on the list is Hermine.

The eye of Hurricane Earl passed directly over buoy 41046 early Wednesday morning. The graphic below shows that 1:10 PM EST even though the eye of Earl was much farther NW, the winds were still 40 MPH with gusts to 49 MPH.

The time graph below wind speed and barometric pressure. The green line is pressure, which shows a classic “V” pattern. Winds increased as the eyewall approached and then dropped precipitously as the eye passed over (approximately 15 knots at the minimum). Winds increased rapidly but were not as high as the southeast eyewall passed over.

Winds reported for hurricane purposes are given in 1-minute time averages for sustained winds and 3 seconds for gusts. The standard observation height is 10 meters. In order to accurately compare measurements, the time average and the height must be standardized. Buoy data is generally reported in 6 minute increments and the anemometer on this buoy was at a height of 5 meters. Thus, standardized winds were higher than the graph below indicates.

The following graphics show expected wind fields. Keep in mind, however, that if the track of Earl shifts east or west, the wind field will obviously shift, as well. The graphics do give an idea of the extent and width of expected winds. The forecast below indicates sustained gale force winds by 8PM Thursday over much of coastal North Carolina.

By Noon Friday, gale force winds could extend from southern Delaware to the central coast of North Carolina (See below).

By Friday at midnight (shown below) winds could be at storm force or above over Cape Cod and gale force from coastal New Hampshire to central Long Island.

By Noon Saturday, storm to hurricane force winds could affect Maine and Nova Scotia with gale force winds further east and west.

Buoy 41047 was NNE of the eye of Earl at 1:23 PM, as shown below. Earl will probably not pass directly over this buoy but winds were 40 MPH gusting to 60 MPH at 1:23 PM with amazingly high 28′ seas.

The water vapor image below shows that dry air has wrapped around the periphery of Hurricane Earl. There will be a balancing act in intensity over the next 24 hours as drier air may try to weaken the storm at the same time as near record warm water temperatures and low shear keep the intensity high.

The enhanced satellite image below shows that there is more than adequate cirrus outflow from Earl. In order to intensify, moist air must be drawn in at lower level and drier air expelled at higher levels.

If Earl and Fiona were not enough, Gaston could threaten the Leeward Islands for a third time. Yet, another wave is moving off of Africa. Could that eventually become Hermine? We”ll see.