From: Andy Soos, ENN
Published September 6, 2012 01:35 PM

Hurricane Isaac

Hurricane Isaac was a slow-moving tropical cyclone that caused severe damage along the northern Gulf Coast of the United States in late-August 2012. Isaac reached hurricane strength the morning of August 28. The storm made its first U.S. landfall at 6:45 p.m. CDT that evening (2345 UTC), near the mouth of the Mississippi River. As it passed through the northern Caribbean, around south Florida, and into Louisiana and the Middle Mississippi Valley, Hurricane Isaac brought lots of rain, some of it beneficial, and some of it not. It is having an impact across all of the eastern US. In some places, it a flood nightmare and in some places it helps relive local droughts.

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The storm caused extensive flooding in Haiti and was blamed for many fatalities.  Rainfall totals were on the order of 120 to 200 mm along the coast of northern Cuba, but over Florida, the totals were much higher. Prior to the rain from Isaac, an upper-level low spawned numerous showers and thundershowers over southeastern Florida. The combination of the two resulted in totals over 160 mm (~6 inches) in central Florida to as much as 320 mm (~13 inches) over Lake Okeechobee.

Rainfall totals from Aug. 27 to Sept. 5, 2012 when Isaac came ashore in southeast Louisiana and moved up into Missouri. The highest totals over land for this period were in southeast Louisiana, southeast Mississippi, western Alabama, and southeast Florida with totals anywhere from 120 mm to upwards of 320 mm (~5 to 12.6 inches).

New Orleans reported up to 508 mm (20 inches) of rain. Isaac was blamed for five fatalities in Louisiana and two in Mississippi. Farther north, however, Isaac did help to bring some beneficial rains to parts of the drought-stricken Midwest with rainfall totals on the order of 40 to as much as 120 mm (~2 to 5 inches) spread across northern Missouri, Illinois, Indiana and Ohio.

The 2010—2012 Southern United States drought is a severe to extreme ongoing drought plaguing the US South, including parts of Texas, Oklahoma, Kansas, Colorado, New Mexico, Arizona, Louisiana, Arkansas, Mississippi, Alabama, Georgia, South Carolina, and North Carolina. The worst effects have been in Texas, where near-record drought has parched the state since January 2011.   The hurricane lessened that drought at least  in the eastern states.

Katrina of course will always be remembered for the massive storm surge that inundated large portions of the northern Gulf coast, reaching almost 28 feet  along the Mississippi coast, breaking the previous mark of 24 feet . Like Katrina, Isaac was also a large storm with both measuring roughly 248 miles in size. Big storms have bigger wind fields, which allow them to push against the ocean surface over a large area, increasing the potential for storm surge for a given area of coastline.

Fortunately, Isaac impacted the coast as a much weaker Category 1 hurricane and was a tropical storm prior to that; Katrina made landfall as a much more powerful Category 3 storm and was previously an extremely powerful Category 5 storm. At one point, Katrina had hurricane force winds extending up to 75 miles from the center. So far preliminary reports indicate that Isaac's storm surge may have reached up to 12 feet in parts of Louisiana, which is quite substantial for a "mere" Category 1 storm. Of course the surge can vary according to the shape of the coastline and seafloor, but 12 feet  is more in line with a Category 3 storm than a 1 and shows how size can be an important factor.

For further information see Rainfall.

Hurricane Isaac image via NASA.

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