NASA's TRMM Satellite Sees Heavy Rainfall in Hurricane Alex

Hurricane Alex is generating some very heavy rainfall, and the Tropical Rainfall Measuring Mission satellite known as TRMM has been calculating it from its orbit in space. As predicted by the National Hurricane Center (NHC) in Miami, Florida, Alex intensified after entering the warm waters of the southwest Gulf of Mexico.

The TRMM satellite's data on June 29, 2010 at 9:50 a.m. EDT showed some heavy rain (red) falling at up to 2 inches per hour, spiraling toward Hurricane Alex's center. The yellow and green areas indicate moderate rainfall between .78 to 1.57 inches per hour. Credit: NASA, Hal Pierce

At NASA's Goddard Space Flight Center in Greenbelt, Md., scientists created an analysis of Alex's rainfall using data captured by the TRMM satellite on June 29, 2010 at 1350 UTC (9:50 a.m. EDT). At that time the sustained winds around Alex were estimated to be 60 knots (~69 mph). Alex continued to strengthen and was classified as a hurricane early on 30 June 2010. This made Alex the first hurricane in the 2010 Atlantic hurricane season.

The rainfall analysis used TRMM Precipitation Radar (PR) data and TRMM Microwave Imager (TMI) data. The TMI data showed that a heavy band of precipitation (some areas showed rain falling at more than 2 inches per hour) was spiraling into the center of Alex's intensifying circulation. The precipitation analysis was overlaid on visible and infrared data from TRMM's Visible Infrared Scanner (VIRS). In this image a Geostationary Operational Environmental Satellite (GOES East) visible image was used to fill in locations not viewed by the TRMM satellite.

The TRMM satellite's data on June 29, 2010 at 9:50 a.m. EDT showed some heavy rain (red) falling at up to 2 inches per hour, spiraling toward Hurricane Alex's center. The yellow and green areas indicate moderate rainfall between .78 to 1.57 inches per hour. Credit: NASA, Hal Pierce Alex is expected to continue to be a large rainmaker when it makes landfall. Rainfall accumulations are expected of between 6 and 12 inches, with isolated amounts of 20 inches.

Tropical Storm-force winds are expected to reach coastal areas in the warning areas this afternoon, while hurricane-force winds will reach the coast tonight. In addition, the National Hurricane Center noted "a dangerous storm surge will raise water levels by as much as 3 to 5 feet above ground level along the immediate coast to the north of where the center makes landfall."

By 11 a.m. EDT, Alex was still a category one hurricane with maximum sustained winds near 80 mph. Alex was located about 145 miles (235 km) east of La Pesca, Mexico and 190 miles (310 km) southeast of Brownsville, Texas. That makes Alex's center near 23.8 North and 95.5 West. Alex is moving northwest at 7 mph (11 km/hr), and has a minimum central pressure near 961 millibars.

Satellite data show that Alex is a large hurricane and the hurricane force winds extend outward up to 60 miles (95 km) from the center. Tropical storm force winds extend outward up to 200 miles (325 km) primarily to the northeast of the center.

The National Hurricane Center noted today that "Given such a low minimum pressure...the current satellite presentation and a favorable environment for intensification...the winds should increase today and Alex could reach category two before landfall."

Tropical Storm Alex intensified by 11 p.m. EDT on June 29 and became the first hurricane of the 2010 Atlantic Ocean Hurricane Season. NASA satellites continue to provide visible, infrared and microwave satellite data to forecasters to help the National Hurricane Center forecast Alex's intensity and track, and NASA's Aqua satellite flew over Alex hours before it became a hurricane yesterday.

The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument that flies aboard NASA's Aqua satellite is one of those NASA instruments that provide forecasters data. MODIS captured a visible image of Alex on June 29 at 3:35 p.m. EDT as it churned over the Gulf of Mexico, and provided a high resolution image of this large storm's extent in the Gulf of Mexico.

Now that Alex has become a hurricane, the storm has the title of being the first June hurricane in the Atlantic Ocean since 1995.

A hurricane warning is in effect for the coast of Texas south of Baffin Bay to the mouth of the Rio Grande and the coast of Mexico from the mouth of the Rio Grande to La Cruz. A tropical storm warning is in effect for the coast of Texas from Baffin Bay to Port Oconnor, and the coast of Mexico south of La Cruz To Cabo Rojo.

At 8 a.m. EDT, Hurricane Alex's center was closing in on the Mexican and south Texas coasts. Alex's center was located about 155 miles (250 km) east of La Pesca, Mexico and 220 miles (355 km) southeast of Brownsville, Texas. That puts Alex's center near latitude 23.4 north and longitude 95.3 west. Alex is moving toward the west-northwest near 7 mph. The National Hurricane Center calls for a "A slow west to west-northwestward motion over the next 24 to 48 hours."

The Hurricane Center forecast says that on the forecast track the center of Alex will approach the coast of northeastern Mexico or southern Texas by late this afternoon or early evening, and Alex will make landfall in the hurricane warning area late tonight or early Thursday morning.

Maximum sustained winds remain near 80 mph so Alex is a category one hurricane on the Saffir-Simpson Hurricane wind scale. Additional strengthening is forecast and Alex could become a category two hurricane prior to landfall.

The National Oceanic and Atmospheric Administration's buoy 42055 located southeast of Alex recently reported sustained winds of 54 mph with a gust of 63 mph.

Smaller hurricanes have higher pressures, and larger hurricanes tend to have lower pressures. Alex is a very large hurricane and has a minimum central pressure near 959 millibars. Hurricane force winds extend outward up to 25 miles from the center and tropical storm force winds extend outward up to 200 miles. Flood watches stretch from New Orleans to southern Texas because of the size of Hurricane Alex.

Source: Rob Gutro
NASA's Goddard Space Flight Center