November 09, 2009
Ida, currently a strong tropical storm with maximum sustained winds just below hurricane strength at 61 knots (70 miles per hour), is shown in these side-by-side images from NASA's QuikScat satellite and the Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua satellite.
In the left-hand QuikScat image, acquired Nov. 9 at 3:23 a.m. PST (11:23 UTC), the white barbs show the direction of Ida's winds and point to areas of heavy rain. The highest wind speeds are shown in purple. QuikScat uses microwaves to peer into a storm's clouds and determine wind speed and direction. QuikScat confirmed that Ida's tropical storm force winds extend outward up to 322 kilometers (200 miles) from the storm's center.
The right-hand AIRS infrared image shows how the storm looks through AIRS' infrared window channel, which measures the temperature of Ida's cloud tops or the surface of Earth in cloud-free regions. The lowest temperatures in dark purple are associated with high, cold cloud tops that make up the top of the tropical storm.
Ida is expected to transition to non-tropical status after making a predicted landfall on Tuesday, Nov. 10 on the northern Gulf coast. It is then predicted to veer sharply east. Rainfall totals of 8 to 13 centimeters (3 to 5 inches), with local amounts of up to 20 centimeters (8 inches), are possible from the Gulf Coast northward into the eastern Tennessee Valley and the southern Appalachians. Large and destructive waves will accompany a storm surge of 1 to 1.5 meters (3 to 5 feet) near the point of landfall.
Since the National Oceanic and Atmospheric Administration's National Hurricane Center began keeping records in 1851, only 62 tropical storms have formed in the month of November, of which just more than half became hurricanes. Of those, only five storms have made a U.S. landfall; the last was Hurricane Kate in 1985. Atmospheric and oceanic conditions typically become unfavorable to hurricanes in the Gulf by November. Ida's weakening on Nov. 9 is attributed to wind shear (winds blowing at different levels in the atmosphere that can tear storms apart) and cooler waters. Tropical cyclones need sea surface temperatures of 27 degrees Celsius (80 degrees Fahrenheit) or warmer to maintain strength.
Links to: http://www.nasa.gov/mission_pages/hurricanes/archives/2009/h2009_Ida.html