Subject: (Sam) Houston, we (may) have a problem... Date: Thu, 01 Aug 2002 22:22:28 -0400 From: "James Franklin" Organization: NOAA/Tropical Prediction Center To: Mark Powell , Peter Black , Brian R Jarvinen , Colin J Mcadie , James M Gross , John L Beven , Richard J Pasch , Edward N Rappaport , Christopher Landsea , James Franklin CC: Michael L Black I decided to see what could be gleaned from the existing dropsonde data base with regard to Mark's idea that increased roughness decreases the surface winds close to shore. I was able to identify a group of sondes released in Georges from about 03Z-13Z on 28 Sept 1998 at its final landfall. I identified 6 sondes released about 50-60 km offshore (03-08Z), and a second group of 6 sondes within 10 km of shore (07-13Z). (Landfall occurred at 1130Z.) The off-shore sondes (first attachment) were mostly in the SE eyewall, the near shore sondes mostly in the E eyewall. I have attached plots of the wind speed in the lowest 1000 m for each group. While there is certainly variability, to my eye the near-shore sondes have a much sharper dropoff of wind in the lowest 200 m than do the sondes far from shore. (John Guiney noted in his preliminary report that GPS sondes at landfall showed a sharp low-level wind reduction.) This is, of course, just one case, and I don't know if there are other factors that could explain this apparent difference in structure. I will look further at the data set to see if there are opportunities for additional similar comparisons (perhaps Bonnie). James -- James L. Franklin Hurricane Specialist, National Hurricane Center (note: return to wordperfect document for graphs originally attached to this e-mail)