Tom says:

You are the only person i know that consistantly talks about the MJO which seems to be a MAJOR driver for tropical development. Thanks!!

Eric Webb says:

@Mech 7002
I’m not so sure about Katrina, but I have something interesting about Hurricane Andrew’s somewhat unexpected intensification in relation to a major equatorial Kelvin Wave in August 1992. When I actually went and looked back into the SOI daily data files, available at http://www.longpaddock.qld.gov.au/seasonalclimateoutlook/southernoscillationindex/soidatafiles/DailySOI1887-1989Base.txt I made quite a discovery. Since I have always wondered in awe at the rapid intensification of Hurricane Andrew over the Atlantic, I’ve always pondered how this came to be, perhaps I may have found the underlying cause to this storm’s intensification. I don’t know if any of you know this, but there has been significant research into the study and effect of Kelvin Waves on hurricane intensification. Generally, as depicted by the picture below, equatorial Kelvin Waves, and their propagation eastward across the global tropics is unique in that as they move into a certain region, they have a tendency to lower the atmospheric pressure and enhance thunderstorm activity over the tropics. In doing so, this forces air to rise upwards and outwards in the upper levels of the troposphere to compensate for the rising motion near the surface. On the frontward edge of such Kelvin Waves (would be in the middle of this picture below), note how as air is first being driven upward while the surrounding air mass in front is continuing to spread out. Well, if you actually think about it, in this precise region on the edge between the downward and upward Kelvin Wave, divergence is the greatest in the upper levels of the atmosphere, and when you consider that in hurricanes the upper levels of the storm must be able to properly “evacuate” air out of the lower regions of the atmosphere and spread out in all directions in the upper levels in order to allow more air to rush in near the surface, and strong divergence aloft is extremely favorable for hurricanes. Now, consider this point and look at a depiction of the equatorial Kelvin Wave so you can have some idea of what i’m talking about here. Notice in the middle, where the Kelvin Wave actually is, (lower pressures in the wake of the Kelvin Wave, with higher pressures in front) if a hurricane is at that point, air will spread out in both directions from that location aloft, giving extremely favorable upper level atmospheric conditions to allow for strengthening, potentially rapid at that, for hurricanes. When I actually looked into the daily data for SOI in August of 1992, this is what came up 1992 229 1016.33 1013.65 6.45
1992 230 1015.74 1012.85 7.73
1992 231 1014.39 1012.35 2.52
1992 232 1013.11 1012.35 -5.20
1992 233 1012.20 1013.20 -15.90
1992 234 1012.27 1013.30 -16.06
1992 235 1011.77 1013.10 -17.93
1992 236 1012.08 1012.55 -12.69
1992 237 1013.99 1012.75 -2.33
1992 238 1014.51 1013.20 -1.86 – See more at: http://weatheradvance.com/2013/03/24/hurricane-season-forecast-late-winter-ramblings/#sthash.zbjr3hjd.dpuf