After crossing the Yucatan Peninsula of Mexico, Hurricane Dean emerged into the Gulf of Mexico as a Category 1 storm late in the day on 21 August 2007. GOES-12 10.7µm IR imagery (above) shows a ragged eye associated with Dean; also note the burst of convection to the north and northwest of the eye (beginning around 00:45 UTC on 22 August). This area of convection continued to increase in areal coverage, with IR brightness temperatures eventually cooling to -80º C / -112º F (black enhancement).

An AWIPS image of the MODIS Sea Surface Temperature (SST) product from 20 August (above) reveals a region of warmer SST values in the general area where the convective burst was seen to form on the IR imagery above. SST values were as warm as 86.7º F / 30.4º C (dark red enhancement), and this pocket of deep, warm water may have helped to fuel the burst of convection.

MODIS true color imagery of the Yucatan Peninsula before Dean (above) and after Dean (below) show that the hurricane winds increased the levels of turbidity in the waters of the Gulf of Mexico, leading to widespread areas of cyan and milky-colored water off the west coast of the Yucatan (due to a large amount of suspended particulate matter in the water).

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GOES-12 IR images (above) from the CIMSS Tropical Cyclones site show Hurricane Dean making landfall along the Yucatan Peninsula region of Mexico during the early hours of 21 August 2007, with sustained surface winds near 165 mph. Dean was the first Category 5 storm to make landfall in the Atlantic Basin since Hurricane Andrew struck Florida back in 1992, and Dean’s central pressure at landfall (906 hPa) was the 3rd lowest pressure at landfall (behind 892 hPa with the 1935 Labor Day Hurricane in the Florida Keys, and 888 hPa with Hurricane Gilbert near Cancun, Mexico in 1988). While the appearance on satellite imagery (and the loss of a well-defined eye) indicated a rapid weakening after landfall, Dean is expected to maintain hurricane intensity as it traverses the Yucatan Peninsula.

An IR image from polar-orbiting NOAA-18 satellite (below) shows the eye of Hurricane Dean about 1 hour prior to landfall. Station identifier MMCM is Chetumal, Mexico. The coldest IR brightness temperatures in the northern eyewall region were -83º C / -117 º F (dark red enhancement), while IR brightness temperatures within the eye region were as warm as +20º C/ 68 º F.

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The GOES-12 IR image (above) and the SSM/I 85GHz brightness temperature image (below) from the CIMSS Tropical Cyclones site show Hurricane Dean shortly after it was upgraded to Category 5 intensity late in the day on 20 August 2007, with surface winds estimated to be about 160 mph. Dean is the first Category 5 storm in the Atlantic basin since Hurricane Wilma in October 2005.

Note the double eyewall structure indicated on the SSM/I image below.

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AWIPS images of the DMSP and POES AMSU rainfall rates along with the GOES-12 IR channel imagery (above) shows Hurricane Dean as a Category 4 storm in the western Caribbean during the morning on 20 August 2007. Satellite-based rainfall rates within the spiral bands of the hurricane were as high as 35 mm per hour (1.4 inches per hour), and GOES-12 IR brightness temperatures around that time were as cold as -77º C (-107ºF). Dean continued moving westward across the Caribbean, steered by easterly winds along the southern periphery of a deep layer ridge that was centered over the southeastern US. Refer to the CIMSS Tropical Cyclones site for the latest information on Hurricane Dean.

An animation of GOES-12 visible images (above; Java animation) shows the eye of Dean. When viewed using the normal operational GOES image interval of 15 minutes, the low cloud features within the eye appear to be rotating anticyclonically (clockwise). This is an optical illusion, similar to the “strobe effect”: the low clouds in the eye are moving so quickly that their true motion can only be determined by viewing images more frequently than once every 15 minutes.

Fortunately, GOES-12 was placed into Rapid Scan Operations (RSO) mode beginning at 18:55 UTC, so images after that time were available at 5 to 10 minute intervals. The GOES-12 RSO visible image animation (below; Java animation) shows the low cloud features within the eye rotating in the “correct” direction (cyclonically, or counterclockwise).

A visible image from NOAA-18 (below) provides a closer view of the mesovortex cloud features within the eye of Dean. Use this Java image fader applet to fade between the NOAA-18 visible image and the corresponding NOAA-18 IR image.

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