The typical view of a hurricane shows cloud structure, but these unique images show the three-dimensional distribution of rainfall within Hurricane Irene. Made from data from the radar on the Tropical Rainfall Measuring Mission (TRMM) satellite, the images cover Irene’s development from a tropical storm on August 21 to a Category 3 hurricane on August 24. The images also show the locations of TRMM-observed lightning flashes, which are indicated with yellow circles. These views of the storm’s inner core provide insight into the hurricane’s structure, which can help forecasters predict how the storm will develop.
For example, lightning in the inner core generally suggests the presence
of strong updrafts and large ice particles. By implication,
lightning suggests that convective cells are pumping a lot of
latent heat energy into the tropical cyclone’s central vortex,
which is favorable for intensification. Hurricane eyewalls
often are devoid of lightning, as is the case for Irene on August 23, 2011 (center image).
Category 3 Irene on August 24 (lower image) did have lightning flashes in the
eyewall, and there were many flashes during Irene’s tropical
storm phase on August 21 (top image).
On Sunday, August 21, Irene was only a tropical storm, and the TRMM
Precipitation Radar reveals that it had an impressive hot tower
that reached over 9.5 miles high (15.75 km). Strong radar
signals, perhaps from large ice particles are shown in red at
the base of the hot towers, which suggests strong updrafts were
present in order for the ice particles to have time to grow large.
Strong rain had yet to completely encircle the eye, as is typical
of tropical storms. Because such towering clouds feed energy into the storm, they are a sign that the storm is likely to intensify.
On Tuesday, August 23, (center) Irene was a category 1 hurricane, in the
process of intensifying to category 3 in less than 12 hours.
Consistent with intensification, the TRMM radar showed that Irene
had a complete eyewall circling its eye along with a region of
intense convection on the eastern side of the eyewall (right
side of image). Some studies suggest that bursts of convection
in one portion of a hurricane’s eyewall may help to pump latent
heat into a hurricane and thereby assist with intensification.
By mid-day Wednesday (lower image), Irene had reached the status of a “major” hurricane, at Category 3 strength. The observations of the TRMM
radar show a compact eyewall, with the possibility that an outer
eyewall is forming. Double eyewalls can be part of an eyewall
replacement cycle associated with changes in hurricane intensity,
either increases or decreases that are difficult to predict.
Lightning was detected in the eyewall, further evidence of the
energy that convection is pumping up from the ocean into the