NASA's Tropical Rainfall Measuring Mission (TRMM) satellite saw tropical cyclone Garry moving through the open waters of the South Pacific Ocean on January 25, 2013 at 0909 UTC (4:09 a.m. EST). Tropical Cyclone Garry was classified as a category two tropical cyclone on the Saffir-Simpson hurricane scale a couple hours earlier but had started to weaken when TRMM flew over. Sustained wind speeds were estimated to be less than 85 knots (~98 mph) and Garry is forecast to continue weakening while moving toward the southeast.
TRMM's main mission is to measure rainfall over tropics but has frequently been useful for monitoring tropical cyclones. The rainfall data compiled on Tropical Cyclone Garry was from two TRMM instruments. Rain rates in the Garry's center were taken from the TRMM Precipitation Radar (PR), the first precipitation radar in space, while rain rates in the outer swath were taken from the TRMM Microwave Imager (TMI). The heaviest rainfall was occurring in Garry's eastern quadrant at a rate of 2 inches (50 mm) per hour.
TRMM's Microwave Imager (TMI) is a passive microwave sensor designed to estimate rainfall in an 878 km (~545.6 miles) wide area by measuring the amount of microwave energy emitted by the Earth and its atmosphere. TRMM PR has a horizontal resolution at the ground of about 5.0 km (~3.1 miles) and sees a strip of the earth that is 154 miles (247 kilometers) wide.
TRMM PR can peer through obscuring clouds and provides 3-D vertical profiles of rain and snow from the Earth's surface up to a height of about 12 miles (20 kilometers). The 3-D and rainfall imagery is created at NASA's Goddard Space Flight Center in Greenbelt, Md.
Steering the Storm
The upper levels of the atmosphere are a major factor in the life and behavior of a tropical cyclone. Forecasters at the Joint Typhoon Warning Center (JTWC) analyzed the upper levels of the atmosphere above Garry and found that the system is deeply embedded in the prevailing westerly winds. Those upper level winds are contributing to Garry's intensification.
By Jan. 27, a trough (elongated area) of low pressure is expected to approach Garry and change its direction to a more east-southeasterly direction.
As Garry moves further to the south, forecasters at JTWC expect vertical wind shear to increase and make the storm decay. Garry is expected to become an extra-tropical cyclone over the next couple of days and become a cold core low by Jan. 29.