Tag Archives: hurricanes

Isaac’s Impact on U.S. Drought

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The worst drought in fifty years has been plaguing America’s agricultural heartland all summer. Earlier this week, however, the soggy remnants of Hurricane Isaac brought some much needed relief to the situation, if only in a small area.

According to the U.S. Drought Monitor, between two and six inches of rain fell across the Mid-West. As a result, the region’s severe drought status improved from 50% to 45%. While this precipitation was beneficial to area’s soybean crop, which is still maturing, it arrived too late to save the region’s fields of desiccated corn.

To quench this drought completely, experts say another five to fifteen inches of rain is still needed.

Image Credit: US Drought Monitor

Hurricane Isaac

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Hurricane Isaac, the ninth named storm of this Atlantic Hurricane Season, made landfall in Louisiana late Wednesday.  Despite its humble category–one status, this storm severely battered the Gulf Coast for several days.

Measuring nearly 250 miles in size, Isaac was a massive storm.  It produced strong winds and high storm surge that caused power outages and significant property damage throughout the region. Moving slowly – at approximately 5 mph – Isaac also brought unrelenting heavy rain, which lead to widespread flooding. According to the NWS, rainfall totals for this storm, so far, range from 10 to 20 inches across the area. The communities of Plaquemines Parish, LA and Slidell, LA were particularly hard hit by rising water.  In Mississippi and Alabama, several hurricane-induced tornadoes have also been reported.

Downgraded to a tropical depression, the remnants of Isaac are now moving inland.  Forecasts predict this enormous system will bring drenching rainfall to the drought stricken regions of the mid-west and southern plains.   Unfortunately, however, this storm could bring too much rain too quickly to the parched land and possibly cause flash flooding in some areas.

Similar to last year’s Hurricane Irene, Hurricane Isaac demonstrates that even low-category hurricanes can pack a serious punch.

Hurricane Isaac, 2012

Image Credit: NOAA

Hurricane Irene: One Year Later

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One year ago today, Tropical Storm Irene made landfall in New York City and roared through the northeastern United States.

Originally a category-one hurricane, Irene was a massive storm that left a trail of destruction from North Carolina to Maine.  Locally, the storm dumped 6.87 inches of rain on NYC and caused widespread power outages.  Most of Irene’s impact, however, was felt further inland.  Drenching rains in the mountains of upstate New York and interior New England caused extensive and catastrophic flooding.  In the end, Irene claimed the lives of 58 people across 13 states and caused approximately $16 billion worth of damage.

Today, Hurricane Isaac, another category-one “i” storm, is bearing down on the Gulf Coast.  While every hurricane is unique, the enormous size of this current storm is reminiscent of Irene.

Hurricane Irene, 2011

Image Credit: NOAA

Tropical Storm Debby

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Tropical Storm Debby, the fourth storm of this Atlantic Hurricane Season, has been battering Florida for days.  Spawning more than two dozen tornadoes, Debby’s strong winds have caused power outages and significant property damage around the state.  The most serious problems, however, are being produced by this storm’s relentless precipitation.

Essentially stalled over the Gulf of Mexico since Saturday, Debby has unleashed torrential rain and high storm surges up and down the Florida peninsula, causing widespread flooding.  The northern and central parts of the state have been particularly hard hit. According to the NWS office in Jacksonville, rainfall totals for this storm, so far, range from 15 to 20 inches across northern Florida.

Stretching out 205 miles from its center, this massive and slow moving storm finally made landfall late this afternoon. It is forecast to travel across the state and move out into the Atlantic Ocean by the end of the day tomorrow.  Before leaving, however, Debby is expected to unload even more rain on the already saturated Sunshine State.

It is hard to believe that many parts of Florida were suffering under serious drought conditions only a few weeks ago.

The Saffir-Simpson Scale for Rating Hurricanes

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Hurricanes are one of nature’s most powerful storms. When formed in the Atlantic Ocean or North-Eastern Pacific, they are rated according to the Saffir-Simpson Scale.

Developed in the early 1970’s by Herbert Saffir, a civil engineer, and Dr. Robert Simpson of the National Hurricane Center, the scale classifies hurricanes into five categories based on the strength of their sustained winds.  Each category is considered an estimate of the potential damage that a storm will cause if it makes landfall.  As conditions change within a storm, its category is re-assessed.

The different categories, 1 through 5, represent increasing wind speeds and escalating degrees of damage.  Since its introduction, the NHC has modified the Saffir-Simpson Scale a number of times.   In fact, earlier this year they refined the wind speed range for categories three through five.  These changes are reflected in the chart below.

Chart Source: NOAA

Naming Hurricanes

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People have been naming hurricanes, informally, for centuries. Past identification schemes included naming storms after Christian saints or the location that suffered the most damage. Today, when a tropical cyclone’s winds exceed 39 mph, it is classified as a tropical storm and assigned a name from a pre-determined list.

Naval forecasters began using unique names for storms during WWII in an effort to avoid confusion when multiple storms were on the map.  Shown to improve communications, this system was adopted by the NWS in 1953.  Originally using only female names for storms, the list was diversified in 1979 to include male names.  Today, the World Meteorological Organization produces the alphabetical lists and the order of male and female names alternates every year.

The WMO maintains a set of six rotating lists for each hurricane-prone region around the globe. After a six-year cycle, names are re-used.  Names are only retired when a storm was particularly noteworthy – causing a large number of fatalities or an extraordinary amount of damage. Some retired Atlantic Basin names include: Andrew, Katrina, and Irene.

Below is the list of names for the 2012 Atlantic Hurricane Season. Note that names beginning with Q, U, X, Y, and Z are omitted from this list, as they are in short supply.

Chart: Weather Gamut

How Hurricanes Form

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Hurricanes, named after the ancient Mayan god of wind, are known as the greatest storms on Earth. Referred to as typhoons or simply cyclones in other parts of the world, they develop under different conditions than an average storm.

Producing powerful winds and heavy rain, hurricanes are mature tropical cyclones that have progressed through a number of stages.  Defined by wind speed, these stages include:

  • Tropical Depression: wind speed of 38 mph or less
  • Tropical Storm: winds range from 39-73 mph
  • Hurricane: winds of 74 mph and above

Regardless of their ultimate size or intensity, all tropical cyclones start off as a tropical disturbance – an unorganized cluster of thunderstorms – over a large body of warm water.  These convective storms generate a column of rising air and an area of low pressure. As moisture-laden tropical air sweeps in to fill the low-pressure void, the storm grows and its winds strengthen. Rising upward, the incoming humid air cools and causes water to condense which releases huge amounts of latent heat. This newly freed heat causes air to rise up even further, producing more condensation and extracting additional heat. Through this process the storm system is able to continuously fuel itself.

Subject to the Coriolis Effect, a mature tropical cyclone is essentially a spinning collection of thunderstorms. Once designated as a hurricane, the storm is ranked on the Saffir-Simpson Scale according to its wind speed. A hurricane’s strongest winds are found in the eye wall, the area that surrounds the storm’s calm eye and point of lowest pressure.

Numerous tropical disturbances develop every year, but only a few grow into full-blown hurricanes. According to NOAA, an average of six hurricanes develop in the Atlantic Ocean annually.

NOAA satellite image of Hurricane Daniel (2006)

Image Credit: NOAA

2012 Atlantic Hurricane Season Forecast

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The 2012 hurricane season is off to an active start.  Two storms have already been named and the season does not officially begin until Friday.

Tropical cyclones, known as hurricanes in the United States, can develop around the globe at different times of the year. In this country, we are most affected by the Atlantic hurricane season, which runs from June 1 through November 30.  Peak activity, however, is usually in late August to mid- September.

A hurricane season is an extended period of time in which the majority of storms are likely to develop. This tends to happen in the summer months, when the temperature difference between the sea surface and the air aloft is greatest.

NOAA is forecasting a near-average number of storms this year, despite the pre-season arrival of Alberto and Beryl. Below are the details of NOAA’s forecast for the 2012 season.

Chart Source: NOAA

Atlantic Hurricane Season 2011

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Last week, as the month of November came to a close, so did the Atlantic Hurricane Season.  The six month season was extremely active this year with nineteen named storms. Only two, however, left their mark on the US.

Irene was a category-one hurricane that struck in late August.  The massive storm affected most of the eastern seaboard from North Carolina to Maine. In New York City, she dumped 6.87 inches of rain and caused extensive power outages.  Most of Irene’s sting, however, was felt in the interior sections of the Northeast and New England. Heavy rain in the mountains of upstate NY and Vermont led to catastrophic in-land flooding.

Tropical Storm Lee made landfall in Lousiana in early September.  This large, slow-moving storm brought significant amounts of rain and flooding to the states along the Gulf Coast.  Lee also sparked numerous tornadoes as it moved through the region.

These two storms are reported to have claimed 77 lives and caused an estimated $11 billion in damage.