MIAMI, Aug 26 (AFP) - Hurricane Katrina relentlessly pounded storm-weary Florida, killing at least three people, leaving about 1.5 million homes without power and collapsing a Miami highway overpass. Hours after the deadly storm slammed ashore in densely populated southeastern Florida, its eye headed out over the Gulf of Mexico early Friday, but howling winds and pounding rain still battered Miami and surrounding areas. Weakened to a tropical storm as it moved inland, Katrina regained hurricane strength soon after reaching the warm gulf waters where it was expected to strengthen further, causing concerns in oil markets where crude prices reached record highs on Thursday. Katrina packed maximum sustained winds of 128 kilometers per hour as it landed 22 kilometers north of Miami, with gusts reaching 140 kilometers per hour.

Hurricane Katrina track, from NOAA.

Map of affected area with Envisat acquisitions marked, from the University of Wisconsin.

NEW ORLEANS, Louisiana, Aug 29 (From AFP) - Hurricane Katrina, the rain from which is already lashing New Orleans, was downgraded early Monday to a category four storm, but forecasters warned it could strengthen again before it hits the city, a US government weather service reported. The National Hurricane Center said the monster storm now packed sustained winds reaching 155 miles an hour, slightly weaker than necessary to qualify for category five status. "But Katrina is expected to make landfall as either a category four or possible a category five hurricane," the center warned. At 0700 GMT, the eye of the storm was located 113 kilometers south of the mouth of the Mississippi River and about 209 kilometers from New Orleans. Highways were gridlocked during the night as tens of thousands of people fled New Orleans and other coastal areas. Because much of the city of 1.4 million people is below sea level, it is highly prone to flooding. New Orleans Mayor Ray Nagin fears flood embankments might not withstand the ferocity of the hurricane.

Analyses of Hurricane Katrina courtesy of Professor J. Fischer, Institute for Space Science, Free University of Berlin:

This Medium Resolution Imaging Spectrometer (MERIS) image acquired on 25 August 2005, shows Hurricane Katrina over Florida and Cuba.

These two Medium Resolution Imaging Spectrometer (MERIS) images acquired on 28 August 2005, show Hurricane Katrina over the Gulf of Mexico. In the first image the coastlines have been highlighted to help define the affected areas.

This Advanced Synthetic Aperture Radar (ASAR) Level 1 image, was acquired on 28 August 2005 over the Gulf of Mexico, presenting a different view of the hurricane.

This comparison image examines the two different views of Hurricane Katrina acquired by the ASAR and MERIS instruments on 28 August 2005.

This animation presents another comparison between the radar and optical images.

The damaged Interstate 10 bridge over Lake Ponchartrain which joins the Metairie area of New Orleans to Mandeville on the north shore of the lake is clearly visible in this ASAR image acquired on 31 August 2005. The I-10 twin span bridge was blown over and partially destroyed by Hurricane Katrina. Some sections were missing while others had shifted position. The waters of Lake Ponchartrain at centre image and Lake Maurepas just to the west continued to rise on 30 and 31 August, while levees were breached and floodwaters poured into the centre of the city. The hardest-hit areas are located in the centre of the city, while slightly higher ground south of the Mississippi near the Lac des Allemands was less inundated. As the image shows, very little of the city escaped the floodwaters. About 80% of the city's total area was left under water.

Flooding in the Metairie area of New Orleans is visible in this ASAR image acquired on 31 August 2005, following Hurricane Katrina. Most of New Orleans lies below sea level and is protected by canals, walls, dykes and pumps. The areas of the city which were flooded by as much as six metres of water after two levees or dykes burst on 30 August on canals leading to Lake Pontchartrain. Lake waters continued to rise on 30 and 31 August and water poured into the city as pumps had failed. The circular area of the New Orleans Superdome, where thousands of trapped residents sheltered during the worst of the hurricane, is barely visible to the northwest of the double span of the Greater New Orleans Bridge, across the Mississippi from the Algiers Point Revetment at the first bend of the river at the right edge of the image. Water was waist-high in the area when this image was acquired. The area west of City Park, the dark area at centre image just east of the I-10 Bridge bordering on the Orleans Outfall Canal, also appears to be heavily flooded. Both airports were also under water.

This Envisat (IMP) radar image was acquired on 06 September 2005, and shows the city of New Orleans days after the flooding that occurred following Hurricane Katrina's passage.

This quick look is a colour composite of a PROBA CHRIS acquisition taken on 03 September 2005 over the city of New Orleans. The three bands of CHRIS PROBA (610-680 nm, 500-590 nm, 469 - 499 nm) are associated to the RGB bands of this colour composite. The dark brown areas correspond to probable flooded areas and to cloud shadows. The space resolution at Nadir is 18m, and the swath size about 14km.

Credit: Image processing by Sira Technology Ltd, UK, 2005

This ERS-2 multi-temporal image was created with a colour composite of three different acquisitions. The three layers are associated by;

• Red: Orbit 52771 - 24 May 2005
• Green: Orbit 53272 - 28 June 2005
• Blue: Orbit 54274 - 06 September 2005