The 2011 Atlantic hurricane season has been busy so far in terms of tropical storms with seven named storms; however, none of them have had a very large impact. Each has been small, short-lived or remained at sea, and none have intensified into a hurricane until Irene reached hurricane status on August 22.

The Tropical Rainfall Measuring Mission (TRMM) satellite passed directly over Irene as the storm moved westward toward the Dominican Republic from Puerto Rico. The images were taken at 15:57 UTC (11:57 AM EDT) on August 22, 2011.

The top image shows a top-down view of the rain intensity within the storm. TRMM reveals that although a hurricane, Irene has not yet developed an eye and is not yet fully organized. The center of the storm is located just to the southwest of an area of heavy rain (shown in red) about midway between Puerto Rico and the Dominican Republic. Rainbands, containing light to moderate rain (shown in blue and green, respectively) curve around the storm mainly to the north and east of the center, revealing the presence of the storm’s low pressure circulation, but one that is not yet intense.

Rain rates in the center of the swath are from the TRMM Precipitation Radar and those in the outer swath are from the TRMM Microwave Imager. The rain rates are overlaid on infrared data from the TRMM Visible Infrared Scanner.

The lower image, taken at the same time, provides a three dimensional perspective the storm. It reveals an area of deep convection (shown in red) near the storm’s center where precipitation-sized particles are being carried aloft. These tall towers are associated with strong thunderstorms responsible for the area of intense rain near the center of Irene seen in the previous image. They can be a precursor to strengthening as they indicate areas within a storm where vast amounts of heat are being released. This heating, known as latent heating, is what is drives a storm’s circulation and intensification.

At the time these images were taken, Irene was a Category 1 hurricane with maximum sustained winds reported at 70 knots (about 130 kilometers per hour or 80 miles per hour) by the National Hurricane Center. Irene is expected to turn to the northwest towards the central Bahamas and intensify where it could become a major hurricane.

Irene, which originated from a tropical wave that propagated off the west coast of Africa, became the 8th named storm of the season as it approached the Lesser Antilles on August 20 and the first hurricane of the season as it was passing over Puerto Rico on the morning of the 22nd. Now back over open water, Irene is poised to pass close to the northern coast of Hispaniola and poses a threat to the Bahamas.

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

Images produced by Hal Pierce and caption by Steve Lang and Hal Pierce.