Hurricane Ivan Discussion Number 28
Statement as of 5:00 am EDT on September 09, 2004
Air Force recon this morning has found an intense Hurricane Ivan.The central pressure of 922 mb has dropped 15 mb in the past 7hours...while the 700 mb flight-level winds have increased to 154kt...equal to 139 kt surface wind...to the north and northeast ofthe center on two separate passes. In addition...and eyewalldropsonde recorded a wind speed of 175 kt at about 630 ft above sealevel. Based on this information...Ivan is easily upgraded to a140-kt category 5 hurricane. As I write...a new recon reportindicates an extrapolated pressure of 916 mb.
The initial motion is 290/13. Ivan has been slowly gaining latitudeover the past 24 hours...and the last two recon fix positionssuggest that Ivan may be moving at 295 degrees. Dropsonde data fromthe 00z synoptic surveillance flights around Ivan has resulted in tight agreement among all of the available NHC models through 60hours...on Ivan moving over or at least very near Jamaica in 36-48hours. After that...the models diverge considerably...although thespread is much less than it has been over the previous 2-3 days.Unfortunately...the model spread still brackets the FloridaPeninsula. The main difference between the models again remains inhow they handle the development and future track of a mid- toupper-level low currently near 34n 48w. Water vapor winds suggestthat the upper-low is stronger than all of the models have beenforecasting. However...the model that initialized the low the bestat 00z was NOGAPS. This model has been very consistent...along withthe ECMWF model...on bringing Ivan across west-central Cuba andthen over or near the Florida Peninsula. The UKMET model remainsthe westernmost outlier...while the GFS is still the easternmostoutlier. However...both models have been gradually shifting theirtracks toward Florida...and the latest GFDL run now takes Ivanacross Southeast Florida in 96-120 hours. Given the betteragreement among the models on this forecast cycle...the officialtrack is close to the previous forecast through 72 hours...and thenshifted slightly eastward at 96- and 120-hr.
The upper-level outflow pattern is impressive and well-established...And if anything...will only get better for the next 72-96 hours.Therefore...the future intensity will likely be modulated by inner-core convective changes and land interaction since th water ahead ofIvan is only forecast to get warmer...as warm as 30c south of Cubaand over the Florida Straits. Click below for current track forecast...http://www.wunderground.com/tropical/tracking/at200409_model.html