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Hurricane Katrina Discussion Number 18
Statement as of 5:00 PM EDT on August 27, 2005
reports from Air Force Reserve and NOAA hurricane hunter aircraft... as well as the Key West WSR-88D...show that Katrina is still in a concentric eyewall cycle with the inner eyewall 9 N mi wide and the outer 45-50 N mi wide. The central pressure has risen as high as 950 mb...with the latest central pressure at 945 mb. The aircraft have found flight-level winds as high as 119 kt at 8000 ft in the outer eyewall...although measurements from the NOAA stepped frequency microwave radiometer suggest the surface winds in this area are still less than 100 kt. The initial intensity remains at 100 kt for this advisory. The initial motion remains 275/6. Katrina is south of a deep-layer ridge over the northern Gulf Coast. This ridge is forecast to weaken as a strong deep-layer trough develops over the central United States...and a new deep-layer ridge forms over the Florida Peninsula and the adjacent Atlantic. This pattern change should cause Katrina to turn northward during the next 72 hr and make landfall over the northern Gulf Coast. Track guidance remains in agreement with this scenario...although the GFS and GFDL have led an overall shift to the west toward southeast Louisiana. This
shift is not unanimous...however...as the UKMET has shifted to the east of its previous track. The new track is nudged just a little to the west of the previous track...along the west edge of the main cluster of guidance for the firs 24-36 hr and down the middle of that cluster thereafter. The track calls for landfall in southeast Louisiana in a little under 48 hr.
Katrina should strengthen as it comes out of the concentric eyewall cycle. The GFDL is now calling for a peak intensity of 131 kt... while the SHIPS model is calling for 130 kt and the FSU superensemble 128 kt. The intensity forecast will call for strengthening to 125 kt at landfall...and there remains a chance that Katrina could become a category five hurricane before landfall. There remains the possibility of another concentric eyewall cycle before landfall...which could throw off the intensity forecast a bit. The new forecast track and wind radii require a Hurricane Watch for and expanded portions of the northern Gulf Coast at this time. Hurricane warnings will likely be required later tonight for parts of the watch area. Forecaster Beven