Tag Archives: storms

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

Pineapple Express

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A Pineapple Express is a non-technical term used to describe a weather pattern that originates in the tropical Pacific and impacts the west coast of the United States. More specifically, it is a type of atmospheric river.

According to NOAA’s Earth System Research Laboratory, atmospheric rivers are “relatively narrow regions in the atmosphere that are responsible for most of the horizontal transport of water vapor outside of the tropics.” Coming in a variety of shapes and sizes around the globe, they form when strong winds associated with storms draw moisture into a thin area ahead of a cold front. The strongest atmospheric rivers can carry as much as 15 times the amount of water that flows through the mouth of the Mississippi River.

Directed by the jet stream, a Pineapple Express transports moisture from the Hawaiian tropics to the west coast of the US. They are famous for bringing warm, moist air and heavy rain to California, Oregon, and Washington. Just a few of these events, according to NOAA, can supply the region with 30% to 50% of its annual precipitation. While beneficial on one hand, they can also be dangerous. If these systems stall over an area, they can cause major flooding and landslides.

The term Pineapple Express is named for the tropical Pacific’s popular fruit.

The atmospheric river known as the pineapple express. Image credit: cimss/wunderground

The atmospheric river known as the pineapple express.  Image credit: cimss/wunderground.

Rev. 2014

Mammatus Clouds

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Clouds are visual indicators of what is going on in the atmosphere.  They are also aesthetically interesting.

Mammatus clouds are one of the more striking sights in the sky. Technically, they are a supplementary feature of a variety of other large clouds. However, they are most dramatic when they line the underside of a cumulonimbus. Shaped like giant udders, they form when parts of the anvil cool and sink into warmer air.  In general, the more plump the udders, the more severe the recent or nearby thunderstorm.

Below is a photo of the remnants of the first Mammatus cloud I ever saw in person. It was taken in New York City shortly after a violent summer thunderstorm a few years ago.

Photo Credit: MF at the Weather Gamut

How Tornadoes Form

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Generated by severe thunderstorm activity, tornadoes are nature’s most violent storms. Scientists do not know exactly what causes them, but atmospheric instability and wind shear are important contributing factors.

Instability in the atmosphere is created when a warm, humid air mass meets a cool, dry air mass.  Through the process of convection, this encounter allows warm air to rise easily and produce thunderstorms.  The greater the instability, the stronger a thunderstorm can become.

Wind shear occurs when there is a localized change of wind speed and direction.  When surface winds blow in one direction and upper level winds in another, the air in-between is set in a horizontal rolling motion.  The updraft of the thunderstorm can then tilt the rotating air into a vertical position.  When that vortex extends from the cumulonimbus cloud to the ground, a tornado is born.

Tornadoes can occur anywhere in any season, but are more typical in the spring and summer months in the United States.  According to NOAA, approximately 1,200 tornadoes touch down in this country every year.

Severe Weather: Watches and Warnings

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Severe weather can happen anytime of the year, given the proper conditions.  This past weekend, for example, unstable air and wind shear combined to send tornadoes roaring through America’s heartland.

Any meteorological event that can cause property damage and loss of life is categorized as severe. It can come in a variety of forms, depending on location and season.  High winds, strong thunderstorms, tornadoes, wildfires, dust storms, hurricanes, floods, and blizzards are all examples of severe weather that occurs in the United States.

When any severe weather event is in the forecast, it is important to understand the difference between the various alerts issued by the National Weather Service.  They include advisories, watches, and warnings.  All should be taken seriously.

  • Advisory:  An “advisory” is issued when significant, but not severe, weather conditions are likely to occur. Residents should exercise caution.
  • Watch:  A “watch” is issued when dangerous weather conditions are possible over the next several hours.  They generally cover a large geographic area.  Residents should be prepared to take action.
  • Warning:  A “warning” is issued when dangerous weather is imminent or already occurring.  They cover a smaller, more specific geographic area.  Residents should take action immediately.

Texas Tornado Outbreak

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Tornadoes swept across northeast Texas yesterday afternoon.  Widespread damage and numerous injuries have been reported, but luckily no fatalities.

So far, the National Weather Service has confirmed that eleven twisters touched down in the Dallas-Fort Worth metroplex, the ninth-largest metropolitan area in this country. The strongest storm in this outbreak was rated an EF-3 on the Enhanced Fujita Scale. It tore through the Dallas suburb of Forney, TX with winds of up to 150 mph.

Video taken during this outbreak shows the incredible power of a tornado’s winds, both horizontal and vertical. The footage of 8-ton tractor-trailers being lifted over one hundred feet in the air and tossed around like toys is unforgettable.

It is sadly coincidental that this devastating storm occurred on the anniversary of the Super Outbreak of 1974, the most violent tornado outbreak in U.S. history.

Tractor-trailers being sent skyward by the lifting power of a tornado near Lancaster, TX

Image credit: KXAS

The Enhanced Fujita Scale for Rating Tornadoes

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Tornadoes are nature’s most violent storms.  They damage or destroy everything in their path, including weather equipment.  Therefore, in order to gauge the strength of a tornado, experts use the Enhanced Fujita Scale.  It infers wind speeds from the damage left in the wake of a storm.

Dr. Ted Fujita, a severe weather research scientist at the University of Chicago, developed the original Fujita scale in 1971. The National Weather Service used it from 1973 until 2007, when they adopted the Enhanced Fujita scale. A commission of meteorologists and structural engineers formulated the new model.  It maintains the original scale’s six categories, but refines their wind speeds to reflect differences in construction quality and improved damage survey techniques.

The different categories, EF-0 through EF-5 represent increasing wind speeds and escalating degrees of damage.

Chart Data: NOAA

Deadly March Tornado Outbreak

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Roaring through the Ohio and Tennessee Valleys this past weekend, tornadoes claimed the lives of forty people across five states.  This was one of the deadliest March tornado outbreaks in the U.S. since 1950.

At this point, the National Weather Service has confirmed forty-five twisters in eleven states.  This number, however, is likely to rise as damage investigations continue.  The strongest storm in this widespread outbreak was rated an EF-4, the second highest ranking on Enhanced Fujita Scale. With winds of 175 mph, it devastated the town of Henryville, IN. Another hard hit area was West Liberty, KY. An EF-3 storm, with winds of 140 mph, is reported to have charged through the town’s main street, destroying everything in its path.

Tornadoes, nature’s most violent storms, are spawned by severe thunderstorm activity.  They can occur anywhere in any season, given the proper conditions. That said, they are more typical in the spring, when the atmosphere is transitioning from cold winter weather to summer warmth.

With the spring equinox just around the corner, this tornado season is only getting started.   Unfortunately, more severe weather is likely in the coming months.

Image Credit: NWS/Storm Prediction Center

First Snow of 2012 in NYC

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On Saturday, New York City received 4.3 inches of snow in Central Park.  This was our first significant snowfall of the season.  The city’s last measurable snowfall was back in October during a surprising pre-season snowstorm.

This winter has been relatively mild, so it was exciting to finally see some snow on the ground.  The local forecast, however, is calling for a major warm up this week.  As a result, this snow will not last long.  However, with more than two months left to the winter season, I am guessing that the snow will be back before long.

Central Park's Lake frozen and covered in snow.

The Sheep's Meadow in Central Park covered by a blanket of snow.

Photo Credit: MF at The Weather Gamut