Karen recently became the eleventh named storm of the 2007 Atlantic hurricane season. There are about 10 named storms in an average year with 6 typically becoming hurricanes. Although the peak of the Atlantic season, which is around mid-September, is now past, October can still be a fairly active month. The season officially runs through November.

The 12th tropical depression (TD #12) of the season originated from an area of low pressure in the central Atlantic during the night of 24 September 2007 (local time). Systems that form this far east are known as Cape Verde storms. They are more common in the middle of hurricane season as warmer waters expand farther east towards Africa. On the morning of the 25th, TD #12 was upgraded to Tropical Storm Karen. With plenty of warm water available, Karen started to show signs of strengthening on the morning of the 26th; however, later that day the system began to encounter strong southwesterly wind shear and stopped intensifying.

The image on the right was taken by the Tropical Rainfall Measuring Mission satellite (known as TRMM) at 01:19 UTC 27 September (9:19 pm EDT 26 September) 2007 and shows Tropical Storm Karen as it was moving west-northwest through the central Atlantic about 1100 miles east of the Windward Islands. The image shows the horizontal pattern of rain intensities estimated from TRMM satellite data. Rain rates in the center swath are based on the TRMM Precipitation Radar (PR), and those in the outer swath on the TRMM Microwave Imager (TMI). The rain rates are overlaid on infrared (IR) data from the TRMM Visible Infrared Scanner (VIRS). The effects of the southwesterly shear are readily apparent. Nearly all of the rain, including several areas of heavy rain (shown by the darker reds), is displaced northeast of the center of circulation (denoted by the tropical storm symbol). This disruption to the storm's structure greatly inhibits its ability to strengthen as the heat released by the active convection (associated with the moderate to heavy rain) is blown downstream away from the center of circulation. At the time of this image, Karen's maximum sustained winds were reported at 60 knots (69 mph) by the National Hurricane Center. The system is expected to slowly weaken as a result of the ongoing wind shear and turn more northward away from the Caribbean.

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