GOES-13 10.7 µm IR images

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 µm 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).

DMSP SSMIS 85 GHz microwave image

Katia existed in an environment of relatively low 850-200 hPa deep layer wind shear (below), which was one factor that favored further intensification.

GOES-13 IR image + Deep layer wind shear product

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.

ASCAT scatterometer surface winds

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MODIS true color Red/Green/Blue (RGB) images

A sequence of daily 250-meter resolution MODIS true color Red/Green/Blue (RGB) images from the SSEC MODIS Direct Broadcast site (above) showed the development and evolution of the smoke plume emanating from a swamp fire that was burning in the Bayou Sauvage National Wildlife Refuge near New Orleans during the 26 August – 31 August 2011 time period. The change in daily wind directions resulted in very different smoke dispersion patterns on each day. Smoke from this fire caused air quality alerts to be issued for the New Orleans and Baton Rouge areas.

AWIPS images (below) of the 1-km resolution MODIS 0.65 µm visible channel data at 19:16 UTC (2:16 pm local time on 30 August) showed the curving smoke plume; about 9.5 hours later, the fire “hot spot” (black to red to yellow color enhanced pixels) was seen on a 1-km resolution MODIS 3.7 µm shortwave IR image at 04:42 UTC (11:42 pm local time on 30 August).

MODIS 0.65 µm visible image + MODIS 3.7 µm shortwave IR image

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GOES-13 Visible (0.63 µm) images (click image to play animation)

An area of disturbed weather that emerged off the coast of Africa over the weekend has acquired sufficient organized convection to be classified as a Tropical Storm, Katia, the 11th named storm of this active Atlantic Hurricane Season. Analyses from the CIMSS Tropical Weather Website show the storm just south of a region of dry air from the Sahara. Shear analyses at the site show that Katia is projected to move into a region of decreasing shear in the next 24 hours. In addition, sea surface temperatures are warm. The forecast from the National Hurricane Center suggests slow strengthening over the next 3 days.

Overshooting Tops diagnosed with MSG data (click image to play animation)

Overshooting tops diagnosed using MSG data (at this site) (above) show a decrease in OT generation over the center of the system today, coincident with warming of the cloud tops. Variability in the number of OTs is common, as shown here.

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MODIS true color images: 16 August and 28 August 2011

Heavy rainfall associated with Hurricane Irene included 20.40 inches at Virginia beach, Virginia and 20.00 inches at Jacksonville, North Carolina (HPC summary). Winds gusted as high as 115 mph at Cedar Island, North Carolina. The effects of the heavy rain and strong winds can be seen in a before/after comparison of 250-meter resolution MODIS true color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above). On the “before” image (16 August 2011), there was a large smoke plume seen from a fire that was burning in the Great Dismal Swamp area in far southeastern Virginia; on the “after” image (28 August 2011), water turbidity was significantly enhanced due to suspended sediment across the Outer Banks region of North Carolina — and a narrow filament of sediment was being actually being entrained into the flow of the Gulf Stream.

AWIPS images of the corresponding MODIS 0.65 µm visible channel data and the MODIS Sea Surface Temperature (SST) product (below) showed that the enhanced turbidity features seen on the MODIS true color image generally exhibited slightly cooler SST values (in the middle to upper 70s F, blue color enhancement) compares to the waters located closer to the Gulf Stream (SST values in the lower 80s F, darker red color enhancement).

MODIS 0.65 µm visible channel image + MODIS Sea Surface Temperature image

Farther to the north, another before/after MODIS true color image comparison revealed additional areas of sediment being carried off the coast of the Northeast US (below). Also note that there was a great deal of sediment in the Hudson River (perhaps better seen in this 20 August / 29 August comparison).

MODIS true color images: 26 August and 29 August 2011

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