Archive for the ‘Extratropical cyclones’ Category
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THE ENTIRE FIRST PARAGRAPH THAT FOLLOWS IS A DIRECT QUOTE FROM DR. JEFF MASTERS (PICTURED BELOW) THAT WAS CUT AND PASTED FROM HIS WEATHER UNDERGROUND SITE; DR. MASTERS IS MY MOST RELIABLE AND DEPENDABLE SOURCE WHEN IT COMES TO TROPICAL WEATHER; HE IS A DEDICATED ‘WINNER:” ONE REASON WHY I DEPEND SO HEAVILY UPON HIS WORK IS THAT HE IS NOT OPERATING UNDER THE CONSTRAINTS OF NATIONAL WEATHER SERVICE FORECASTER BUT HE BENEFITS FROM THEIR INTERPRETATIONS AS WELL AS FROM OTHER NATIONAL WEATHER SERVICE RESOURCES. HE IS DEDICATED, “UP FRONT,” AND RESPONSIBLE.
The forecast for Ida –
Posted: 10:21 AM EST on November 08, 2009
“The high wind shear of 20 – 25 knots currently affecting Ida is forecast to persist at that level until Monday night. Some slow intensification is still possible while Ida remains over the exceptionally warm water of the Loop Current in the Gulf of Mexico, through tonight (Figure 2). Late tonight, Ida will be crossing over waters of 26°C, which is barely enough to support a hurricane. With shear still expected to be at 20 -25 knots, I expect weakening to begin early Monday morning and accelerate on Monday afternoon. At that time, Ida will encounter 40 knots of wind shear associated with a cold front over the Gulf of Mexico, and begin transitioning to an extratropical storm. Exactly how strong Ida will be when it reaches the coast early Tuesday morning–and indeed if Ida even does reach the coast–is a forecast with high uncertainty. The computer models have a tough time forecasting the evolution of a tropical cyclone into an extratropical cyclone, and the models are all over the place on what will happen. Most of the models foresee a landfall near 1 am EST Tuesday between Mississippi and Pensacola, Florida, then a path northeastward over the Southeast U.S. However, Ida could come to halt before reaching the coast and turn west towards Tampa (the UKMET model’s forecast), or turn south back over the Gulf of Mexico (the NOGAPS model’s forecast). In any case, storm surge and heavy rain appear to be the main hazards from Ida. The GFDL model (Figure 3) is forecasting rain amounts of 4 – 8 inches for a large swath of the Gulf Coast, and there is a risk of tornadoes if the warm air from the core of Ida pushes ashore.” END QUOTE
From my point of view, (this is Cloudman23 writing) everyone on the Gulf Coast from Mississippi to Key West should have a “heads up” mindset while Ida is out there. As Dr. Masters said, the computer models have a difficult time when the tropical to extratropical metamorphoses takes place. Furthermore, the chance of tornadoes (mentioned by Dr. Masters) in association with warm, moist air from Ida and its inherent instability in such situations, this storm should not be taken lightly.
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: https://cloudman23.wordpress.com/2008/08/30/gfdl-model-a-great-source-for-an-animation/https://cloudman23.wordpress.com/2008/08/30/gfdl-model-a-great-source-for-an-animation/
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