The wind shear which reduced hurricane Katia to a tropical storm has diminished allowing Katia to form a clear eye and a more symmetric circulation. Several objective methods show that Katia has strengthened to an 80 to 85 knot (about 90 to 100 miles per hour) hurricane.
The National Hurricane Center (NHC) has just upgraded Katia to a 100 miles per hour hurricane at 11am. The NHC is forecasting Katia to become a major hurricane as it approaches the passage between the Outer Banks of North Carolina and Bermuda.
FORECAST POSITIONS AND MAX WINDS
INIT 04/1500Z 21.9N 59.2W 85 KT 100 MPH
12H 05/0000Z 22.9N 60.6W 95 KT 110 MPH
24H 05/1200Z 24.1N 62.4W 100 KT 115 MPH
36H 06/0000Z 25.2N 64.0W 100 KT 115 MPH
48H 06/1200Z 26.2N 65.6W 105 KT 120 MPH
72H 07/1200Z 28.0N 68.5W 105 KT 120 MPH
96H 08/1200Z 30.0N 71.5W 105 KT 120 MPH
120H 09/1200Z 33.0N 72.0W 95 KT 110 MPH
A series of microwave images taken in a "window" that sees through the upper deck of clouds to expose the areas of heavy rain show that a tight circular eye formed early this morning. Here's the latest image showing a closed eye and spiral bands.
The new NHC forecast indicates that Katia is likely to miss the Outer Banks and Bermuda, but possibly hit Canada.
However, there has been considerable divergence among models in predicting Katia's strength and track. The NHC's track and intensity forecasts have been repeatedly adjusted. The European model, which is one of the most reliable track models, takes Katia close enough to the outer banks to cause strong damaging surf and currents to the coastline already impacted by Irene. (ECMWF 7day forecast from Ryan Maue's FSU site)
The NHC partially explains the difficulties involved in making the forecast.
KATIA APPEARS TO BE ON TRACK WITH AN INITIAL MOTION OF 305/10 KT.
ALTHOUGH A LOT OF UNCERTAINTY REMAINS IN THE 3 TO 5 DAY FORECAST
PERIOD...LITTLE CHANGE WAS MADE ON THIS FORECAST RELATIVE TO THE
PREVIOUS ONE. THE ECMWF...UKMET...AND HWRF MODELS REMAIN ON THE
SOUTHWESTERN SIDE OF THE GUIDANCE WHILE THE GFS AND GFDL ARE A LITTLE FASTER AND FARTHER NORTH BY DAY 5. MUCH OF THIS DIFFERENCE APPEARS TO BE DUE TO THE POSITIONING OF THE CLOSED MID TO UPPER-LEVEL LOW FORECAST TO DEVELOP OVER THE EASTERN UNITED STATES IN 4-5 DAYS...WHICH THE GFS SHOWS ABOUT 300 N MI FARTHER TO THE EAST AND DEEPER THAN IN THE ECMWF AND UKMET AT DAY 5.
THE OFFICIAL FORECAST IS VERY CLOSE TO THE MULTI-MODEL CONSENSUS AND STILL KEEPS THE HURRICANE AT OR EAST OF 72W.
The NHC didn't explain well that the weather models have been inconsistent in how they predict the lower and mid level wind patterns over the eastern United States will evolve in response to tropical storm Lee. Because these wind patterns will affect the track of hurricane Katia, there is more uncertainty in Katia's track forecast than there was in hurricane Irene's track forecast. The most reliable models are all keeping Katia east of Cape Hatteras, but the margin of error is large in this situation. People living in New England and coastal eastern Canada should keep a close eye on Katia.
UPDATED
This morning's Noon GMT run of the GFS model brings Katia a little bit closer to Cape Hatteras than the previous run. Later in the sequence a trough in the jet stream picks up Katia and takes the storm out to sea, missing Cape Cod and Canada.
However, if Katia's forward speed is a bit lower or if Katia is pulled further west by the trough associated with tropical storm Lee, the wave in the jet stream will pass over Katia and leave it close to north America with weak steering winds. In my opinion (please see BillLaurelMD's comments for a meteorology professional's opinion) this is an extremely unpredictable situation.
UPDATE 2
Katia has continued to strengthen. The NHC raised the estimated wind speed to 90 knots (105mph) at 5pm est.
Objective measures show that Katia may have strengthened to more than 90 knots.
CIMSS's Advanced Satellite Microwave Unit analysis estimates that Katia is becoming a major hurricane of over 100 knots. The NHC is careful to not raise or lower wind speeds too quickly because storms take time to spin up or down, but this estimate shows that Katia is still spinning up.
UPDATE 3
The latest 18Z (GMT) runs of NOAA's 2 hurricane models the GDFL and HWRF models track Katia between Cape Hatteras and Bermuda. The forecast track then swings out to sea offshore of Cape Cod and the coast of Canada.
Surf from Katia reached Topsail Beach and the south facing beaches of North Carolina late this afternoon.