Hurricane Bertha North of Puerto Rico

Created by Roger Edwards, Storm Prediction Center

Here is Hurricane Bertha north of Puerto Rico, as photographed by the GOES-8 weather satellite at 0115 UTC (9 pm ADT or 8 pm EDT), 9 July 1996. This type of infrared image detects varying levels of moisture in the upper troposphere (roughly above the 400 mb pressure level).

In this enhanced water vapor image, color progressions from gray thru bright blue to deep blue indicated more moisture; while black through deep red means drying. Often, areas of strong drying correspond to sinking motion in the upper levels; and areas of high moisture content signal rising motion. Such is cearly the case with this image of Bertha, where tremendous amounts of moisture are being pumped high into the atmosphere near the center of the hurricane. The bright blue dot is the eye, which contains much less moisture than the surrounding CDO (Central Dense Overcast).

Note the broad arc of banded, gray-and-blue enhanced material (cirrus clouds) arcing northward out of the hurricane. This is an upper-level outflow channel, marked by the cirrus arc. This cirrus arc was spiraling outward, away from the storm. As large and intense low pressure areas, hurricanes in the northern hemisphere rotate cyclonically (counterclockwise) from the surface up through most of their depth. However, the very top portion is an anticyclonically (clockwise) rotating high! This is the most efficient way for a hurricane to ventilate itself, releasing air through its top in an outward-spiralling (divergent) anticyclone. In the southern hemisphere, the sense of rotation would be the opposite.

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::::: Hurricane Opal (1995) near peak intensity :::::

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