In light of recent official proclamations that there wasn't sufficient warning that this devastation was coming, I took it upon myself to abstract the essential information from each of the National Hurricane Center's advisories for Katrina from the time it left the west coast of Florida until 24 hours before it made landfall on the Gulf Coast.
All of the data is given below. The summary, in three parts, is:
#1. After leaving Florida, Katrina became a category two hurricane at 11:30 AM on Friday the 26th. At that time it was forecast as a possible category three hurricane in 24 hours. It was forecast to become (dropping the word possible) a category three hurricane at 5 PM on Friday the 26th.
(more below the fold)
It became a category three hurricane at 5 AM on Saturday the 27th. At that time, it was forecast to strengthen in the next 24 hours. It was described as "could become a category 4 hurricane" beginning with the 10 AM update on Saturday. It became a category 4 hurricane at 1 AM on Sunday the 28th. At that time the update said, "some additional strengthening possible." Katrina became a category five hurricane at 7 AM on Sunday the 28th and at that time, it was said that, some fluctuations in wind strength were likely.
#2. At the time of the 11 AM advisory on Friday the 26th, the highest probability for landfall was in the area of Apalachacola, FL. By 5 PM this area was greatly expanded, with nearly an equal probability for Apalachicola as for Louisiana. Even at this time Buras, Louisiana (about 30 miles to the east of New Orleans) had the highest percent of likelihood, although forecasting this far in the future, it was still uncertain. By 11 PM the set of highest probabilities had shifted to Gulfport, MS to Louisiana where it would remain, with the highest probability continuing to be Buras, Louisiana.
#3. Put together this says: By Friday evening a best estimate of category three hurricane was in effect and the hurricane had locked on to its target, eastern Louisiana/Mississippi. The most generous thing that can be said is that, at this distance, the certainty was still low. In this case, the predictions were exactly correct. After 11 PM on Friday, the remaining advisories either confirmed this scenario or made it much worse. The possibility of a category 4 hurricane was first described at 10 AM on Saturday.
The forecasters hit this on the money, early on. Some warning bell didn't ring loudly enough with the right people. The Sunday morning advisories were apocalyptic, but even 36 hours before those the signs of a major disaster were evident.
Posts come in several varieties and I've done a bit of each. This is meant to be a basic resource. Feel free to quote it or place it in another thread.
Timeline. Most likely landfall is less frequently updated and when it is not mentioned, it should be assumed no new prediction has been made. These were abstracted from advisories numbered 11b to 23a and from strike probabilities numbered 12 to 23 from the National Hurricane Center site.
http://www.nhc.noaa.gov/archive/2005/refresh/KATRINA+shtml/145512.shtml?
Friday, August 26
9 AM, EDT. Windspeed/category: 75 MPH / 1 Barometer 987 "some strengthening" expected.
11 AM, EDT Windspeed/category: 80 MPH / 1 Barometer 981 "category 2 by Saturday." Center of most likely landfall: Apalachicola, FL.
11:30 AM, EDT Windspeed/category: 100 MPH / 2 Barometer 971 "some strengthening. Could be cat 3 in 24 hours"
2 PM, EDT Windspeed/category: 100 MPH / 2 Barometer 969 "Could be cat 3 major hurricane on Saturday."
5 PM, EDT Windspeed/category: 100 MPH / 2 Barometer 965 "forecast to become Category 3 major hurricane today or on Saturday." Center of most likely landfall: A very broad area indicative of the shift away from Florida. The cities of Apalachicola, FL to the Buras, LA have about an equal probability.
8 PM, EDT Windspeed/category: 105 MPH / 2 Barometer 965 "forecast to become Category 3 today or on Saturday."
11 PM, EDT Windspeed/category: 110 MPH / 2 Barometer 965 "forecast to become Category 3 in the next day or two." Center of most likely landfall: Gulfport, MS to New Orleans, LA.
Saturday, August 27.
2 AM, EDT Windspeed/category: 110 MPH / 2 Barometer 963 "forecast to become major hurricane today."
5 AM, EDT Windspeed/category: 115 MPH / 3 Barometer 945 "some strengthening is forecast during the next 24 hours." Center of most likely landfall: Gulfport, MS to New Iberia, LA.
8 AM, EDT Windspeed/category: 115 MPH / 3 Barometer 940 "some strengthening is forecast during the next 24 hours."
10 AM, CDT Windspeed/category: 115 MPH / 3 Barometer 940 "some strengthening is forecast during the next 24 hours and Katrina could become a category 4 hurricane." Center of most likely landfall: Gulfport, MS to New Iberia, LA.
1 PM, CDT Windspeed/category: 115 MPH / 3 Barometer 949 "some strengthening is forecast during the next 24 hours and Katrina could become a category 4 hurricane."
4 PM, CDT Windspeed/category: 115 MPH / 3 Barometer 945 "strengthening is forecast during the next 24 hours and Katrina could become a category 4 hurricane later tonight or on Sunday." Center of most likely landfall: Gulfport, MS to New Iberia, LA.
7 PM, CDT Windspeed/category: 115 MPH / 3 Barometer 944 "strengthening is forecast during the next 24 hours and Katrina could become a category 4 hurricane later tonight or on Sunday Center of most likely landfall: Gulfport, MS to New Iberia, LA.
10 PM, CDT Windspeed/category: 115 MPH / 3 Barometer 939 "strengthening is forecast during the next 24 hours and Katrina could become a cat 4 hurricane on Sunday." Center of most likely landfall: Gulfport, MS to New Iberia, LA.
Sunday, August 28.
1 AM, CDT Windspeed/category: 145 MPH / 4 Barometer 935 "some additional strengthening is possible today." Center of most likely landfall: Gulfport, MS to New Iberia, LA.
4 AM, CDT Windspeed/category: 145 MPH / 4 Barometer 935 "some additional strengthening is possible during the next 24 hours." Center of most likely landfall: Gulfport, MS to New Iberia, LA.
7 AM, CDT. Windspeed/category: 160 MPH / 5 Barometer 908 "some fluctuations in strength are likely during the next 24 hours." Center of most likely landfall: Gulfport, MS to New Iberia, LA.
10 AM CDT Windspeed/category: 175 MPH / 5 Barometer 907 "some fluctuations in strength are likely during the next 24 hours." Center of most likely landfall: Gulfport, MS to New Orleans, LA.