Tropical storm Isaac was the first hurricane to make direct
U.S. landfall this year. It was a storm of unusual timing and confusion, which
led to the extreme amount of media coverage over the past week.
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| TS Isaac managed to delay the RNC |
The timing of this system could not have been worse. Earlier
this week Isaac managed to postpone the Republican National Convention in
Tampa, Florida, while school systems in Southern Florida cancelled their Monday
classes. Once all of this mitigation was in place Isaac ironically managed to
spare much of the Eastern coastline of Florida minus the Keys.
Much chaos surrounded the actual projected path of Isaac as
it made its way into the Caribbean. Weather computer models had anything from
the storm brushing up against the Atlantic coast to making direct landfall in
Louisiana. The path of Isaac was directly correlated with the speed and
strength of a high pressure ridge, which was predicted to make its way across
the United States. Three different weather models (complex equations that
predict future conditions of the atmosphere) pushed out different results. The
Canadian Model predicted that this ridge of high pressure would drive Isaac on
a more eastern path into the Atlantic Ocean. The European Weather Modeling
system believed that the ridge would dissipate causing Isaac to break into the
middle of the Gulf of Mexico. The United States weather model, known as the
GFS, predicted a path that would directly impact Florida. These models helped
generate the cone of uncertainty of the system.
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| Wx Models had Isaac making landfall anywhere from New York to Louisiana |
The Weather-computing model that ended up winning out was
the European Model, which has supposedly been the most accurate at tropical forecasting in the recent years. The next difficult task, which meteorologists
faced, was predicting the intensity of the storm. The storm initially was to be
at hurricane strength shortly after passing through the Florida Keys. The
initial hypothesis suggested that Isaac would be a strong category 2 hurricane
at landfall. In order for it to be classified a category 2 storm the winds must
be between 96-110 miles per hour, which brings with it storm surge of 6 -8
feet. Over time, it became evident that the storm was battling dry air
entrainment (dry air entering a moist system) and wind shear (Different direction
or speeds of winds at different levels of the atmosphere, which can cause weak
cloud structure). Both of these factors often inhibit intensification of a
tropical system.
Wind speed slowly intensified while the storm rapidly
dropped in pressure. Pressure of the storm is loosely correlated with a
tropical system’s wind speed. As Tropical Storm Isaac slowly inched his way to
landfall the pressure dropped to a typical category 2 hurricane, which puzzled
many meteorologists. Isaac broke a North Atlantic record for having the lowest
pressure level ever recorded in a Tropical Storm. There was much disagreement among meteorologists as to when it should have been dubbed a hurricane. The
National Hurricane Center felt that the classification system should be a cut
and dry yes or no decision. Others felt that there were winds somewhere in the
system at hurricane strength and that hurricane status should have been issued
early Tuesday morning to urge lingering residents to evacuate low-lying
locations of Southeastern Louisiana.
Early Tuesday afternoon Tropical Storm Isaac upgraded his
status and a hurricane was born. The system’s strongest winds topped out at 80
miles per hour as it slammed the Louisiana, Mississippi, and Alabama
coastlines. The hurricane managed to generate enough surge to top 8 foot
levees, which left many residents on their rooftops awaiting rescue. New
Orleans had rainfall totals that topped 20 inches. Others storm totals can be
seen here:
http://www.nola.com/hurricane/index.ssf/2012/08/isaacs_rainfall_totals_through.html
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| ABC News |
The storm has now transitioned into a Tropical Depression as
it moves into the Midwest just in time for Labor Day weekend. Locations of
Indiana, Ohio, and Illinois should expect a rainfall total ranging from 1-5
inches over the next few days. CNN Money has already released an article
stating that the destruction caused by Isaac could hit 2 Billion dollars in
damage. See here:
http://money.cnn.com/2012/08/31/news/economy/isaac-damages/
Even though
Hurricane Isaac is no more, individuals should be wary for the continuation of
activity in the Atlantic Ocean. The months of September and October are
generally the most active of Hurricane season. The ocean waters are warmest in
the Atlantic and Gulf of Mexico during this time year.
Current MSL pressure analysis from the SPC Mesoanalysis shows the deepening low pressure of 984 hPa located over north-central Illinois progressing northwestward. The black lines (known as isobars, or lines of equal pressure) along the western side of the storm are seen very close to one another; this indicates winds at the surface are beginning to strengthen. Wind speeds of 53 mph have been reported at the Davenport, IA airport. Of course, cold air associated with these gusty winds has allowed for heavy snowfall to occur, prompting blizzard conditions in Iowa and Wisconsin (MCD 2193).
