It's been a busy season so far in terms of tropical storms with seven named storms already in the Atlantic basin; however, none of them have had a very large impact as they have either been small, short-lived or remained at sea and none of them have intensified into a hurricane until now. 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 the 20th of August 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.

The Tropical Rainfall Measuring Mission satellite passed directly over Irene as it was leaving Puerto Rico and captured these unique images of the storm as it moving westward near the Dominican Republic. The images were taken at 15:57 UTC (11:57 AM EDT) on 22 August 2011. The above image shows a top-down view of the rain intensity within the storm. Rain rates in the center of the swath are from the TRMM Precipitation Radar (PR), and those in the outer swath are from the TRMM Microwave Imager (TMI). The rainrates are overlaid on infrared (IR) data from the TRMM Visible Infrared Scanner (VIRS). 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.

The next image from TRMM (above), taken at the same time, provides a 3D 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 (~80 mph) 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.

These images were produced by Hal Pierce (SSAI/NASA GSFC) and the captions by Steve Lang and Hal Pierce (SSAI/NASA GSFC).

Learn more about Irene's formation