Tropical storm Sean and a Mediterranean tropical storm?

Image of a tropical system in the Mediterranean Sea on November 8, 2011. Image Credit: NEXSAT

A very uncommon event occurred just east of Spain in the Mediterranean sea early this week.  An area of low pressure has acquired tropical characteristics. This rarely occurs.

Meteorologists posted remarks about the system in the Mediterranean Sea:


This storm originated as an extratropical low which emerged over the Mediterranean sea.  This storm is considered to be called “Rolf”, and it was east of Spain and south of France.  Satellite images show thunderstorms built over the northeast quadrant of the storm with a clearing in the center of the storm.  Sustain winds are around 40 to 45 miles per hour with gusts over 50 mph.  The storm will be pushing through parts of southeast France Wednesday afternoon (November 9, 2011) and satellite images show less organization as it interacts with land.  Surface temperatures in the Mediterranean Sea are below the threshold for tropical cyclone development, and current temperatures are around 63 Fahrenheit or 17 degrees Celsius. For typical tropical development, temperatures should be over 80 F (26 C).  In a way, this system is more subtropical than tropical, as it contains characteristics of both a nontropical and tropical system.  Systems that develop in cooler waters with these characteristics are referenced as “medicanes.” Could we begin to see an increase in tropical systems in the Mediterranean?  It is possible, especially if sea surface temperatures increase in the future. Systems such as this rarely occur, but it has happened in the past.

Tropical Storm Sean on November 9, 2011 earlier this morning. Image Credit: National Hurricane Center

In the Atlantic, tropical storm Sean became our 18th named storm of the 2011 Atlantic hurricane season.  The life of this system is rather interesting.  Remember the heavy snow across the state of Colorado last week?  The same system that caused the heavy snow across Colorado is now tropical storm Sean.  It pushed into the United States as a mid-latitude cyclone and emerged off the southeast coast of the United States. It has been mainly stationary across this area for the past few days, and it began to acquire tropical characteristics and started to become a warm-core low.  The National Hurricane Center (NHC) classified this as subtropical storm Sean on November 8, 2011.  As of today, Sean has acquired all the elements to become fully tropical.  As of now, Sean is 455 miles (735 Kilometers) southwest of Bermuda with sustain winds of 65 mph and a barometric pressure of 991 mb. A tropical storm warning is in effect for Bermuda. Bermuda can expect rough surf as this system will be quickly picked up by a trough as it accelerates to the northeast.  This is the same trough, or extended area of low pressure, that caused the tornadoes across Texas, Oklahoma, and Louisiana on November 7-8, 2011.

Forecast track of tropical storm Sean from the National Hurricane Center.

Convection is increasing around the center of the storm, and appears to be organizing fairly well.  I would give this system a 70% chance to become a hurricane.  The NHC latest forecast agrees with this idea, as the system continues to show an eyewall forming around the center of the storm (image below).  The pressure reading and increased convection around the storm makes me think this system has a chance to become a minimum hurricane before it pushes west of Bermuda.    Rainfall rates will be rather low with this storm across Bermuda, and the NHC is only forecasting one to three inches. The center of Sean will be far away from Bermuda, so direct impacts are not expected with this storm.  Sean will likely survive another two days before it is picked up and absorbed by the trough currently across the eastern United States.  The Atlantic hurricane season officially ends on November 30, 2011.

Infrared satellite image of tropical storm Sean this evening around 5 p.m. EST. Image Credit: NHC

Bottom line:  A rare “medicane” – or storm with tropical characteristics – formed in the Mediterranean Sea and is producing strong winds and rain across southeast France.  Medicanes in the Mediterranean are uncommon, but they have formed in the past.  Tropical storm Sean could become a hurricane later tonight or tomorrow morning, but it should quickly drift to the northeast.  Bermuda will likely see the outer bands of this system, but a direct hit is highly unlikely.  For more information regarding Sean, please visit the National Hurricane Center.


November 9, 2011

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