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Hilary Spins Up in the East Pacific
Hilary became a tropical depression on the morning of 19 August 2005 (LST) south of the Gulf of Tehuantepec in the eastern Pacific. Favorable conditions allowed Hilary to quickly strengthen, and by the evening of August 19, Hilary was already classified as a tropical storm. The very next day, August 20, Hilary became a hurricane. Fortunately, Hilary remained well south of Mexico as it paralleled the coastline heading in a general west-northwest direction.

The Tropical Rainfall Measuring Mission (TRMM) satellite has followed Hilary's progress across the East Pacific. TRMM was launched back in November of 1997 to measure rainfall over the global Tropics. It has also proven itself to be a valuable platform for observing tropical cyclones.

Image of Hurricane Hilary

Image above: This image was taken at 00:43 UTC on 22 August 2005 (5:43 pm PDT on 21 August 2005) as Hilary was passing well south of the southern tip of Baja California. The image displays the horizontal distribution of rain intensity obtained within Hilary as obtained from TRMM's sensors. Rain rates in the center part of the swath are from the TRMM Precipitation Radar (PR), the only radar capable of measuring precipitation from space. Rain rates in the outer swath are from the TRMM Microwave Imager (TMI). The rain rates are overlaid on infrared (IR) data from the TRMM Visible Infrared Scanner (VIRS). At the time of the image, Hilary was classified a Category 1 hurricane with maximum sustained winds estimated at 75 knots (86 mph) by the National Hurricane Center (NHC). Although, Hilary does not have a well-defined, closed eyewall in its the center, TRMM shows that Hilary has a well-developed circulation as evidenced by the strong banding in the rain bands surrounding the center (green and blue arcs). An area of intense rain (red area) is present in the large rain band south of the center of the storm. Within hours of this image, Hilary was upgraded to a Category 2 hurricane with maximum sustained winds estimated at 90 knots (104 mph) by NHC.

Image of Hurricane Hilary

Image above: This image was taken at 00:28 UTC on August 24 (5:28 pm 23 August PDT) as Hilary continued to move westward away from land. By now Hilary was starting to move over cooler waters and convection within the storm was weakening. TRMM shows that the size of the overall rain area has condensed with most of the rain now occurring on the western half of the storm (blue and green areas). An area of intense rain (darker red area) is still located close to the center just to the southwest, but Hilary's eye is now poorly defined with no rain visible on the eastern side of the center. Cutoff from its supply of warm water and having ingested drier air, Hilary will continue to spin down and weaken. At the time of the image, Hilary's winds were estimated at 70 knots (81 mph) by NHC.

TRMM is a joint mission between NASA and the Japanese space agency JAXA.

Images Credit: Hal Pierce (NASA GSFC)
Steve Lang
Goddard Space Flight Center