Tropical Storm 12L intensified on the evening of 31 August to become Hurricane Katia, the second Atlantic basin hurricane of the 2011 season. GOES-13 10.7 Âµm IR images from the CIMSS Tropical Cyclones site (above) showed the development of deep organized convection both east and west of the storm center.
A DMSP SSMIS 85 GHz microwave image (below) revealed a closed eyewall had formed (although the southern portion of the eyewall was thin and poorly-defined).
Katia existed in an environment of relatively low 850-200 hPa deep layer wind shear (below), which was one factor that favored further intensification.
An AWIPS image of EUMETSAT MetOp ASCAT scatterometer surface winds (below) indicated that the radius of tropical storm force winds had increased since earlier in the day as Katia intensified.