Subject: Re: questions for presenters...continued Date: Wed, 07 Aug 2002 14:31:10 -0400 From: "Richard J Pasch" To: James Franklin CC: "James M. Gross" , Colin McAdie , Ed Rappaport , John L Beven , "Brian.R.Jarvinen" , Chris Landsea , Mark Powell , Peter Black James, I discussed this with Ed. Neither of us recalls what the Andrew reduction factor was originally. However we agreed that 0.80 is probably a reasonable compromise for the "old" (early 90's) factor, so try that. Richard James Franklin wrote: > Jim, Richard: > > If you can tell me what particular reduction factor you would like me to > apply, I will make the diagram using it. Let me know, do you want 80%, 85%, > 82.5%, or what? > > At the time of Andrew, I believe a single reduction factor was applied to > recon data at any altitude. Is this what you would like me to do as well? > > James > ----------------------------------------------------------- > James L. Franklin > > Hurricane Specialist > National Hurricane Center > NOAA/NWS/Tropical Prediction Center > 11691 SW 17th Street, Miami FL 33165 > > Email: James.Franklin@noaa.gov > Ph: 305-229-4475 > Fax: 305-553-1901 > > > From: "Richard J Pasch" > > Date: Wed, 07 Aug 2002 14:05:56 -0400 > > To: James Franklin > > Cc: James M Gross , Colin.J.McAdie@noaa.gov, > > "Edward.N.Rappaport" , "John.L.Beven" > > , "Brian.R.Jarvinen" , > > Christopher Landsea , Mark Powell > > , Peter Black > > Subject: Re: questions for presenters...continued > > > > James, > > > > I know you will have a problem with this request because the "old" flight > > level > > wind reduction factor, from the early 90's, was not well established. We were > > inconsistent, and typically we did not distinguish between different flight > > levels in doing the reduction. However, it probably averaged out to be 0.80 > > or > > 0.85, which is consistent with a general rule of thumb that in those days we > > required at least 80 kt/ 40 kt at flight level for a hurricane/tropical storm. > > > > Richard > > > > James M Gross wrote: > > > >> James, > >> > >> I realize there is little hope for you to fulfill the following request on > >> such short notice, given the fact that you are on mids with two or perhaps > >> three systems to follow. But not knowing your software, let me request it > >> anyway in the hopes that there maybe a chance of fulfilling it. > >> > >> Can you reproduce your Figures 1 and 3 from "The Case for Upgrading > >> Hurricane Andrew to Category 5" where the flight level winds (your solid > >> red/orange triangles) were reduced using the old flight level wind reduction > >> to the surface coefficient used during the early 90's? > >> > >> Thanks for your consideration of this request, > >> > >> Jim > >> > >> James Franklin wrote: > >> > >>> Colin J Mcadie wrote: > >>> > >>>> > >>>> 2) To James: > >>>> Based on your preliminary analysis of dropsonde profiles in coastal > >>>> regions versus those in a purely marine environment, do you now have > >>>> some uncertainty in the use of a constant reduction factor for flight > >>>> level winds in near-coastal regions? > >>>> > >>>> > >>> > >>> Do I have "some" uncertainty? Yes. Mark's raising the issue in and of > >>> itself created some uncertainty. And the results thus far certainly are > >>> consistent with his notion. But both Bonnie and Georges were > >>> weakening at landfall. And the wind speeds in these storms were very > >>> different than at Andrew's landfall. I am not knowledgeable enough > >>> about boundary layer processes to know whether Mark's new take on > >>> roughness lengths makes sense or not, or how the result might apply to > >>> Andrew. So there is "some" uncertainty. > >>> > >>> However, the small sample of sondes (near shore vs offshore) currently > >>> available is not sufficient, in my view, to warrant altering any current > >>> practices. It has been the presumption at NHC for years and years that > >>> oceanic winds impinged on the immediate coastline. My take on Mark's > >>> published work is that he thought so too. The sonde results are solid > >>> for the open ocean. I don't think we should change a long-standing > >>> practice without good evidence to do so. The conclusion to be drawn > >>> from the results so far, I think, is that we need to collect more data, > >>> and in stronger storms, and as soon as possible. > >>> > >>> On the other hand, clearly, it would be awkward to upgrade Andrew now, > >>> based on the current understanding, and in several years (because that's > >>> what it would take, I think, to acquire the necessary data) adjust it > >>> and a whole bunch of other storms downward if it turns out he and Peter > >>> Sparks are right. > >>> > >>>> > >>>> > >>>> 3) To all: How should the apparent strengthening seen in the surface > >>>> pressure and satellite data after the 0810 UTC 162 kt > >>>> flight-level wind be interpreted in terms of the wind field? Also, > >>>> what effect, if any, should the strong cells forming along the coast > >>>> in the northern eyewall have had on the surface wind field at the > >>>> shoreline? > >>> > >>> I indicated in my presentation that I thought my estimates were > >>> conservative, because of the apparent post-last-fix strengthening. I > >>> can't speculate on the effect of the strong cells on the cyclone-scale > >>> wind field. > >>> > >>> -- > >>> James L. Franklin > >>> > >>> Hurricane Specialist, National Hurricane Center > >>> NOAA/NWS/Tropical Prediction Center > >>> 11691 SW 17th Street, Miami FL 33165 > >>> > >>> Email: James.Franklin@noaa.gov > >>> Ph: 305-229-4475 > >>> Fax: 305-553-1901 > > > > -- > > Dr. Richard J. Pasch > > Hurricane Specialist > > Tropical Prediction Center/National Hurricane Center > > 11691 SW 17th Street > > Miami, FL 33165-2149 > > Phone: 305-229-4411, Fax:305-553-1901 > > E-Mail: Richard.J.Pasch@noaa.gov > > > > > > -- Dr. Richard J. Pasch Hurricane Specialist Tropical Prediction Center/National Hurricane Center 11691 SW 17th Street Miami, FL 33165-2149 Phone: 305-229-4411, Fax:305-553-1901 E-Mail: Richard.J.Pasch@noaa.gov