Katrina (August 26, 2005): Into the Gulf

GOES-12 Visible imagery of Katrina

GOES-12 Infrared (IR4) imagery of Katrina

GOES-12 Water Vapor (IR3) imagery of Katrina

At 1:00 am EDT on the 26th, Katrina emerged into the Gulf of Mexico as a tropical storm. One hour later, it had once again obtained hurricane status. Throughout the day, the storm continued on its west-southwestward track, running nearly parallel to the Florida Keys. As a result, much of the Keys received tropical storm force winds for most of the day.

Katrina is captured in this true color image from the MODIS unit on the Aqua satellite at 2:40 pm EDT (1840 UTC), shortly after the Key West radar (KBYX) went offline. At each cross, the maximum sustained winds in knots are on the top and the central pressure in millibars is on the bottom. The thick segment of the track line shows the approximate storm's track for 8/26/05. Notice how the center is still obscured by high clouds.

The storm soon found itself situated beneath a large upper-level anticyclone that dominated the entire Gulf of Mexico. This feature provided excellent upper-level outflow to the system as well as low vertical shear. These factors led to a period of rapid intensification in which Katrina intensified from 65 kt to 95 kt in a 24-h period. Another sign of intensification was the reduction of the radius of maximum winds (RMW) from 20 nmi to 10 nmi, indicating a increased level of organization in the storm. One odd characteristic of the day was the fact that while the average radius of tropical storm force winds (34 kt) and hurricane force winds (64 kt) increased significantly (45% and 120%, respectively) , the average storm force (50 kt) radius increased by only 20%.

This is the same image as above, but fully zoomed out. The large rainband is immediately obvious extending to the south of the storm.

Throughout the day, a large and well-defined rainband moved through the Keys, producing heavy rain as far away as Cuba. A full understanding of the rainband is impossible because the Key West radar (KBYX) suddenly went offline around 2:20 pm and remained offline for nearly 14 hours. This outage occurred right as a particularly intense portion of the large rainband was traversing the radar site. It could be that a sudden gust produced minor damage to the unit. Adding to the suspicion is the fact that some base radar products had one more scan available than other products, which hints the damage occurred right during the middle of the scan.



This loop of base reflectivity (left) and base radial velocity (right) radar data originates from the Miami radar (KAMX) at the beginning then switches to the Key West radar (KBYX). The whole loop spans from 12:00 am EDT to around 2:20 pm, when KBYX suddenly went offline. At the top of each pane is color scale and at the bottom right is the time in EDT. Notice that the radial wind speed color scale now ranges +/- 80 kt instead of the +/- 60 kt range used in the last post. It is important to note the the radar is only capable of measuring velocities between -64 kt and +64 kt, thus the velocity data can only show the extent of the hurricane force (64 kt) winds, even though the maximum winds might be significantly greater. (Click on the image to view the loop at full size)