>The Ups and Downs of Hurricane Bill, eyewall replacements, shear, dry air? and “Maximum Potential Intensity”

Written by on August 21, 2009 in Rest of Europe with 0 Comments

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http://www7320.nrlssc.navy.mil/hhc/watl/hh3.watl.20090821.gif Current 500mb Geopotential Heights
Image sources: http://wxmaps.org/pix/hemi.00hr.html

Hurricane Bill which looked to be on it’s way back up to category 4 status last night with a well defined eye and mesovortices reported circling the eye, has all but collapsed. Long and short of it, Bill is struggling these past 6-12 hours. It comes and goes with an eye, just when it’s better defined, it disappears again. The fight with some shear as well as dry air choking the center and possibly supressing the hot towers surrounding the eye as we see the deep convection limited to only certain sides of the system, Bill is down to a high end cat 2 storm right now and the only thing right now thats making me think this thing will regain strength and getting better organised it because it’s travelling over the warmest waters of it’s journey so far and when looking at the MPI (maximum potential intensity chart) he has warmeer waters ahead of him. Not only warm skin temperatures but deep warmth, allowing for a higher potential intensity. Couple this with a better atmospheric environment, the window is slowly closing but it’s still open for now and an area if light shear is ahead also, it all depends of how structurally sound he is. He appears to be under going a series of eyewall replacements which is holding back time for reintensifying. I think given his continued tracking north and nearing higher, cooler latitudes, Bill now has limitations to restrengthening. His environment by Saturday night into Sunday morning slowly goes down hill as the trough centered over the Ohio Valley is going to create shear into Bill’s environment as he travels in between Bermuda and New Jersey. What’s going to make for a very interesting time is, the warmer-than-normal waters between Cape Cod and Nova Scotia may play a major role in supporting Bill as a substantial hurricane up to Nova Scotia. The trough will not only add shear to Bill’s environment but speed him up and bring him north faster and therefore giving less time to weaken. It is possible for Bill to remain a cat 2 storm just off the south shore of Nova Scotia and with past storms I have seen these things hold together in their structure and strength for longer than expected despite being in waters of only low 70s or even 60s. Bill looks to be steered more by the Bermuda High and will be right up to Nova Scotia rather than the trough, but what if that Ridge builds slightly westward if Bill intensifies just enough to release heat into the upper ridge and therefore strengthen the ridge, building it slightly westward?? That would become very interesting and worrying for New Englanders..
My biggest question right now is, how close does Bill get to New England? Could Bill send hurricane force winds to Cape Cod? Even though many say, no. I believe it’s still possible. There are always surprises and theres going to be here with Bill. 15-25 foot waves are going to batter the shoreline from Virginia, Jersey shore, Long Island to Massachussetts and up to Maine with building swells the farther north you go. As you can see I have added two graphics. Both of which measure what the theoretical “maximum potential intensity” achievable in a hurricane in the Atlantic. Note where Bill is both maximum low pressure and wind speed potential are high where his current location in the western Atlantic is. Where the warmest and deepest elements combined are located, that is where the strongerhurricanes can theoretically become strongest IF and this is surprisngly rare (thankfully) that we managed to marry together a very well devleped and organised cyclone in an area that has the warmest deepest waters in the entire basin and the atmosphere also is vertually perfect, absent of shear and a 200mb anticyclone built over top of the system. Those are the fundamental KEY ingredients that all must come together at the exact same time to allow your Camille’s, Andrew’s, Emily’s, Katrina’s Rita’s, Wilma’s, Dean’s and Felix’s to power to 175 mph category 5 monsters. Once at those intensities, the shear energy release and energy imput to fuel and sustain such a machine is simply astonishing. Your Bill’s and most other storms that form year in and year out will never get anywhere near their maximum potential intensity simply because to get a well formed cyclone into such a perfect ocean-atmosphere environment is so rare, plus the ocean basin normally needs to be in it’s warm phase with other factors in place also.
More on Bill and past storms tomorrow.
Thanks for reading.
-Mark

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