Hurricane Isaac - August 25-September 3, 2012
A tropical wave moves offshore the coast of western African by August 16th. Thunderstorm activity began to organize
with the system over succeeding days. By the 21st, the system became well-enough organized with a defined circulation
center to be declared Tropical Depression Nine well east of the Leeward Islands. Aircraft reconnaissance indicated
the system had strengthened into a tropical storm later that day, named Isaac. Isaac passed to the south of
Guadeloupe as it entered the Caribbean Sea on the 22nd. Slowly becoming better organized, Isaac approached
Hispaniola with an eye feature, crossing the southwest peninsula of Haiti on the 25th.
Isaac became elongated as an upper low developed to its west, developing an east-west surface trough with
Isaac on its eastern periphery. Moving northwest along the north coast of Cuba, Isaac slowly recovered some
intensity while moving through the Florida Straits. A ragged eye occasionally formed with the system, but did
not persist. Isaac grew in scale and strengthened as it moved northwest through the Gulf of Mexico.
Late on the morning of the 26th, Isaac strengthened into a hurricane before approaching southeast Louisiana
that night. It lingered near the coast before making landfall during the early morning on the 29th west of
Port Fourchon, Louisana.
The slow-moving system weakened into a tropical storm that afternoon while drifting northwest through Louisiana.
By the afternoon of the 30th, Isaac weakened into a tropical depression in northern Louisiana. The depression
moved northward through Arkansas and Missouri, before evolving into an extratropical cyclone near Columbia,
Missouri as it interacted with an upper trough across the central Plains during the morning of September 1st.
The low moved slowly eastward, moving across southern Illinois and Indiana before dropping towards western Kentucky
on the night of the 3rd. The system's 700 hPa circulation then split in two, with one portion dropping down towards
the Gulf of Mexico and a second, smaller piece moving eastward, spawning a new extratropical low across Ohio
during the morning of the 4th.
The graphics below show the storm total rainfall for Isaac, which used information from the National Weather Service River
Forecast Centers, Forecast Offices, CoCoRAHS, and Earth Networks/Weather Bug. Following the example set by Jerry
1995), the rainfall collection period ended during the morning of the 4th, once the system split in two. Rainfall across
Florida due to the upper low/surface trough which set up ahead of Isaac during the 24th was not inclued in the graphics.