Archive for the ‘Cold core low’ Tag

Ida’s Current Model Forecasts – 11-7-09

The total amount of thermal energy at the surface in the Western Caribbean is high and wind shear aloft is relative low so it is anticipated that Ida will intensify before striking the Yucatan Peninsula.  The Yucatan does not have the type of topography that we associate with significant weakening of a storm due to friction.  But, read what Dr. Jeff Masters says this morning about the fate of Ida after she enters the Gulf of Mexico:

“Once Ida crosses into the Gulf of Mexico on Sunday night, the storm will encounter much cooler SSTs and a strong trough of low pressure that will dump cold air into the storm and bring 40 knots of wind shear. This will cause Ida to lose its tropical characteristics and become a powerful extratropical storm with 45 – 55 mph winds. It is highly unlikely that Ida will hit the U.S. as a tropical storm, but it could still bring tropical storm-force winds of 45 mph to the coast next week as an extratropical storm.”

As for me, I have been favoring the Geophysical Fluid Dynamics Laboratory Model (GFDL) for the path that Ida will take; currently,  if I had to depend upon only one of the many models, that would be the one – in most instances anyway.  I have no real science to back that up – only my perception based upon experience.  Call it a “gut level” good feeling about the model’s past performance if you will.  Therefore I expect Ida to eventually curve rightward as the GFDL shows in the plot below.  By the time it does I expect it will have lost its tropical characteristics though the winds will still be strong.  In other words, it will become extratropical.  TO GET INSTRUCTIONS ON OBTAINING THE GFDL ANIMATION CLICK ON THE FOLLOWING LINK:

The prefix, extra, means “outside of” or “beyond.”  Extratropical cyclones are sometimes called cold core lows whereas tropical cyclones are warm core lows.  When a tropical cyclone draws in cold air (as usually happens when a front interferes with the storm) it becomes extratropical.  The majority of the world’s extratropical cyclones develop in the middle latitudes (30 degrees to 60 degrees latitude) and for that reason are often referred to as middle latitude cyclones.

Graphic courtesy of Jonathan Vigh of the Department of Atmospheric Science at Colorado State University


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Two independent left clicks should enlarge this image.
Two independent left clicks should enlarge this image.

The storm that is at the North Carolina-South Carolina border may look like a hurricane but it is not. The National Weather Service is calling it a non-tropical cyclone. A more common term for such cyclones is “extratropical cyclone.” “Extra” means “outside of.” This refers to their developing outside of the tropics. Hurricanes are tropical cyclones. Even though in the northern hemisphere they both rotate counterclockwise around a central region of low pressure, tropical cyclones have warm cores and are often referred to as “warm core lows.” Relatively cold air occupies part of most extratropical cyclones and this is most certainly the case with this one. The doublet image of the system that I have prepared which you see (above) shows a visible satellite view of the storm earlier today and compares it with a surface analysis.  The two do not represent exactly the same time but it’s close; 44 minutes separate them. So, it’s a near match.

For those of you who know your frontal symbols, notice that there are three different types of fronts, all three representing boundaries between relatively warm air and relatively cool air. An occluded front arcs out from the center of the storm and there is a warm front whose axis runs ENE-WSW, and a stationary front curving down to the south.

In spite of the fact that it is extratropical and therefore un-named, it has many of the characteristics of a tropical storm.  People located in the storm’s vicinity should be alert to the potential hazards. Also, there is a strong chance that it will interact with tropical storm Kyle in the interesting Fujiwhara effect.  If you are interested in that phenomenon, see the following link and also view the post that followed it (at the next higher post location on the page).  To do that you will need to scroll to the top of the page and click on the “blog” tab.  That will access you to all entries.

Tropical Wave AL 93 Might Dance Within a Few Days!