Let's see if this can be described from an EMF standpoint.
Last night, I described a number of factors, including the wake of Fabian, for a reduced conductivity over oceans where Isabel was moving. Also there is an over all pattern, a global pattern, that first caused the storm to blow up and then has reduced the over all electrical input. The problem is that internally, there is no place for the negative charges in the ionosphere created or retained over the convection of the storm to go. That is because the dielectric of water is about 80 times that of air. With the very high cloud tops the line distance between cloud and ocean is huge and the charges "wrong" for a shorting to occur, so the electrical equallibrium cannot come by strikes, or shorting of direct currrents down to the surface. The only thing left is a formation of something like this, where the center of the ionosphere becomes a POSITIVE point and it is surrounded by a ring of negative voltages which then couples to the ocean surface! That is why the shape of the slits are in lines and not circles.
The electrical dynamic of a point POSITIVE ion event is MUCH different from a point POSITIVE ion event. The comparisions to Andrew are certain to occur, but there are a number of substantial differences. Andrew occurred proximate to Mt. Pinatubo's eruption in the context of extremely high levels of SOx emissions. Those emissions would have increasd the phase change temperature of cirrus clouds, much in the winter if where you live it is could you put salt on your driveway to melt the ice. Andrew may not have had an issue with crossing a track of a previous tropical storm to impact its conductivities on the surface, but the SOx issue was huge in its electrical dynamic, IMHO. This storm, OTOH, had its electrical burst, and now quite clearly is not in the same context and has come to a new equillibrium, as a point POSITIVE ion event.
There are several dangers and differences. First, a point positive event will be less likely to be turned, electrically. That is significant in that the storm seems to be wobbling. This is nothing more than the storm now being more subject to ambiant winds. Last night there was a gap in the HP area to the storms north, and it jogged slightly north or right and now the HP area or ridge is rebuilding and there is actually a noticable left or south turn. If the storm were a point negative event, it would hold its course with MUCH less influence from upper level winds.
The storm also is looking more like a tipped egg than a circle. Again, the voltages from a point POSITIVE event differ and the influence on the cloud behaviors is not as direct. Hence the shape is less circular. However, the winds are largely maintained and the eye as larger presents a much larger area that at landfall, in its present shape, that will cause a damage path. Further, the electrical dynamic will be more stable at landfall because the same conductivities are not required at the surface--indeed the lack of conductivities was the reason this new equallibrium has occurred.
So at least while it is like this, it is very dangerous for the islands because it could erractically move to them and because once there the land won't cause as much immediate instability, and there will be greater wind damage. It should be able to ride out this period of lacking conductivity and regional electrical conditions so if it doesn't landfall, it can soon cause a point EMF again.
From the IR pictures of Isabel it is lost some of its donut shaped red orange cold anomalies today after "blowing up" yesterday and becoming a classic looking catagory 5 storm with t values at 7.0 and 160 mph winds and a bp of 921 mp. Andrew, for instance, had a landfalling bp of 922 mb. This is the first cat 5 in the Atlantic since Mitch, so it IS a big deal.
Isabel is passing over the track of Fabian and hence the CO2 content and temperature of the ocean below the storm has decreased. This results in less CO2 gas exchange with the intense winds that stir the ocean surface and lower relative conductivities as well as a temperature related drop in conductivity. Then, electrically, the massive negative voltage over the eye in the ionosphere cannot couple as well with the ocean surface.
To repeat, I have been saying that a tropical storm is a point negative ion event over its center. There is tons of emperical proof of this. For instance:
http://science.nasa.gov/newhome/headlin ... ep98_1.htm
"Rarely seen lightning fields and purple sprites were detected in the eye of the hurricane by the ER-2 pilot as he flew more than 19.8 km (65,000 ft) above the Atlantic.""
Regarding the dielectric of water compared to cloudless air--this causes the direct currents, or the strikes to be rare:
"Surprisingly, not much lightning occurs in the inner core within about 100 km or 60 mi of the tropical cyclone center. Only around a dozen or less cloud-to-ground strikes per hour occur around the eyewall of the storm...."
http://www.aoml.noaa.gov/hrd/tcfaq/G10.htm
Consistent with this, Burke et al. [1992] has reported the detection of keV electrons and large electric field transients above a hurricane. These various observations all suggest that what is occurring at great depths in the ocean may couple to the ionosphere. The coupling mechanisms was said by them not to be well understood, but it seems probable that "capacitive coupling" through the displacement current my drive conduction currents within the ionosphere [Hale and Baginski, 1987].
Now, while NASA was looking at the ion charge over the eye, Bates et al in Nature published a paper about the partial pressures of CO2 under Felix.
The result, then, of Fabian's trek in front of Isabel, is a decrease in an electrical potential in the cirrus cloud disk between cirrus and ionosphere (ionosphere positive, ocean surface, cirrus negative for lack of ability of separated charges discharging to the surface, which is given a negative charge by the coupling). Hence, the cirrus are not elevated by electrical forces as well. Remember the cirrus are tiny and moving a huge rates of speed, such that even a small force deflecting them upwards will increase their capacity to remain elevated in the cloud disk. The cirrus then have an incredible ability to trap heat underneath them, and make them, from space, appear very cold.
So, the main factors of the blow up and now the decrease in the hurricane's electrical potential would be :
1) the day to night change in the context of a heavy solar wind that brings ion particles from space that aid in the electrical organization of the storm.
2) the SOI reversal from a positive value and conductivity increases from "stirring" of the warm tropical waters in the Pacific and what that means overall electrical conditions in the Altantic. That number from tonight should publish in about two hours. Will update, but today it went down from 19 to 14 positive and there was very strong thunderstorms in South America and West Africa, which would have separated charges and put a more positive ion balance in the ionosphere in the Atlantic region. Think tightening of a guitar string along the ITCZ.
3) Warmer water is more CONDUCTIVE. Everyone knows it has more energy for phase changes BUT few appreciate how much heat is lost out into space in a storm and how much cirrus trap--and what it means for the
cirrus to be elevated so that the do trap IR radiation.
4) The track of Fabian also shook out all the CO2 in the water. It's is like a flat soda. You can't get it to fizz after it has been shaken . . . and that means less electron exchanges from a wind and poor conductivity. So it has to get to those warm SSTs not just because they are warm but also because they will be conductive when they are stirred.
