Monthly Archives: June 2012

Weather and Health: Extreme Heat

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An oppressive heat wave is currently scorching the central region of the United States and is forecast to expand eastward this weekend.  As temperatures soar, it is important to remember that intense heat can cause serious health problems.

According to the CDC, extreme heat – temperatures that are significantly hotter than the average local summertime high – is one of the leading causes of weather related deaths in this country.   Claiming hundreds of lives every year, excessive heat kills more people across the U.S. than hurricanes, tornadoes, floods, and earthquakes combined.

Extreme heat is deadly, because it forces the human body beyond its capacity to cool itself. Linked to overheating and dehydration, heat related illnesses range in severity from mild to life threatening.  Symptoms for each stage include:

Heat Cramps:  painful muscle spasms in the legs and/or abdomen

Heat Exhaustion:  fatigue, weakness, clammy skin, and nausea

Heat Stroke:  rapid pulse, hot and dry skin, no sweating, victim could possibly be
unconscious;  a medical emergency

To beat the heat, the American Red Cross suggests:

  • Avoid strenuous activity
  • Dress lightly
  • Eat lightly
  • Drink plenty of water
  • Replenish salts and minerals lost to perspiration
  • Limit caffeine and alcohol
  • Stay out of the sun
  • Cool off in an air-conditioned building, when possible

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.

Early Summer Heat Wave in NYC

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Summer is off to a sizzling start in the eastern United States this year. The season only officially began on Wednesday and extreme heat is already gripping the region.

In New York City, we experienced our first heat wave of the year with three consecutive days of temperatures rising to the mid-90s. The average high for the city at this time of year is 81°F.  In addition to the searing temperatures, the city also had very high humidity levels, creating oppressive conditions.  According to the National Weather Service’s Heat Index, which combines temperature and humidity readings, it felt like we hit the triple digits in the Big Apple this week.

The dramatic increase in heat and humidity in the region is the result of a dominant Bermuda High. This is a subtropical area of high pressure that ushers in hot, humid air from the Gulf of Mexico to the northeast. This sweltering weather pattern, however, is about to change. A cold front is forecast to arrive this weekend, bringing cooler, less humid conditions to the area.

Summer Solstice

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Today is the June Solstice, the first day of summer in the northern hemisphere. The new season officially begins at 23:09 UTC, which is 7:09 PM Eastern Daylight Time.

Astronomical seasons are the result of the tilt of the Earth’s axis, a 23.5° angle. Today, as summer begins, the northern half of our planet is slanted toward the sun.  This position allows the northern hemisphere to receive the sun’s energy at a more direct angle, warming the region.

Today is also the longest day of the year. Since the winter solstice in December, the arc of the sun’s daily passage across the sky has been moving northward.   Reaching its northern-most position at the Tropic of Cancer today, it stopped.  This phenomenon is where today’s event takes its name – solstice is a word derived from Latin meaning, “sun stand still”.

Beginning tomorrow, the sun will embark on its apparent journey southward and our daylight hours will slowly decrease.

Summer Solstice in Northern Hemisphere

Image Credit: scijink.nasa.gov

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

Monthly Summary: May 2012

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Overall, New York City was warm and soggy this May.  Despite a cool start, we finished the month with an average temperature of 65.1°F, which is 3.1°F above normal.  The stretch of very warm days at the end of the month helped contribute to this above average reading.

Precipitation was above average as well.  The city saw 5.38 inches of rain in Central Park.  That is 1.19 inches above normal.  This was the first time we had above average rainfall since October 2011.  New York City, however, is still 5.41 inches below average for the year.  As a result, the city is currently listed as “abnormally dry” on the U.S. Drought Monitor.

Graph Credit: MF at The Weather Gamut