Just as Irene was finally strengthening into a hurricane, it veered north and east, sparing the US East Coast. Irene continued the record fast pace of the 2005 hurricane season, becoming the earliest 9th named storm, well before peak season in September. Irene was also a Cape Verde storm, just like Emily, originating west of the Cape Verde Islands in the central Atlantic. Storms typically do not form this far east so early in the season as water temperatures in the region are usually not yet warm enough. However, this year this part of the Atlantic has been much warmer than normal early in the season.

After forming into a tropical depression (TD #9) on the 4th of August 2005 in the central Atlantic, Irene moved in a general northeast direction. Unable to intensify because of shear and dry air, the storm moved along as a depression or a weak tropical storm for several days. Irene began to approach the US East coast on the 12th, having passed south of Bermuda, as a moderate tropical storm. Irene became a strong tropical storm on the 13th with maximum sustained winds reported at 70 mph by the National Hurricane Center and began to turn more northward as a result of a weakness in the subtropical ridge west of Bermuda. The next day on the evening of the 14th, Irene finally reached hurricane intensity with maximum sustained winds of 80 mph.

Since its launch back in the fall of 1997, the Tropical Rainfall Measuring Mission (or TRMM) satellite has been providing valuable images and information on hurricanes and tropical cyclones over the Tropics. TRMM captured these images of Irene at 05:43 UTC (1:43 am EDT) on 15 August 2005 soon after it became a hurricane. The first image shows the horizontal distribution of rain intensity within the storm (top down view) as viewed by the TRMM satellite. Rain rates in the inner swath are from the TRMM Precipitation Radar (PR), the only radar capable of measuring rainfall from space. Rain rates in the outer swath are from the TRMM Microwave Imager (TMI). The rainfall pattern is overlaid on infrared (IR) data from the TRMM Visible Infrared Scanner (VIRS). TRMM shows that Irene is in the process of forming an complete eye. At this time, a well-defined partial eye wall is identifiable by the green and red semicircle. The outer rainbands show good banding (green arcs), a good indication of a well-developed circulation. The rain field is asymmetric with the bulk of the rain remaining on the eastern side of the storm (blue area), while a well-defined area of intense rainfall (red area) lies in the northeastern portion of the eyewall. This intense rain near the center of Irene is a good indication the storm will try to strengthen. As water vapor condenses into the cloud droplets that produce rain, heat is released. This heat, known as latent heat, is what drives the storm's circulation and is most effective when it is released near the core of the storm.

The second image was taken at the same time and shows the height of the precipitation columns within Irene (defined by the 15 dBZ isosurface). It shows that the intense rain visible in the previous image is associated with an area of deep convection as denoted by the taller red towers. The tallest tower is about 17 km high. These high towers can be a sign of future strengthening as was the case here. Irene intensified to 80 knots (92 mph) later on the 15th, before starting to weaken as the system moved over cooler waters and began to encounter westerly wind shear.

VERY LARGE [4.4 mb] Precipitation Radar slice QUICKTIME animation	VERY LARGE [3.9 mb] Precipitation Radar slice QUICKTIME animation
LARGE [1.8 mb] Precipitation Radar slice QUICKTIME animation	LARGE [1.9 mb] Precipitation Radar slice QUICKTIME animation

VERY LARGE [4.8 mb] Precipitation Radar slice QUICKTIME animation	VERY LARGE [5.0 mb] Precipitation Radar slice QUICKTIME animation
LARGE [1.8 mb] Precipitation Radar slice QUICKTIME animation	LARGE [1.9 mb] Precipitation Radar slice QUICKTIME animation

TRMM is a joint mission between NASA and the Japan Aerospace Exploration Agency (JAXA).

Images produced by Hal Pierce (SSAI/NASA GSFC) and caption by Steve Lang (SSAI/NASA GSFC).