13 September, 2010

See our Facebook & Twitter pages here for weather snippets and more, become a fan today!



Today's Top Weather Stories
On Weather & Climate Through the Eyes of Mark Vogan
 
It's all about whether Igor will top category 5 status at this time
By Mark Vogan
 
It is certainly a beautiful "looking" storm but perhaps not so beautiful underneath it. In looking at it's overall appearance and looking at it's stats, brought to us via the National Hurricane Center, it appears as though it's got a window of oppertunity here to become the first category 5 storm since Felix in September 2007 which made landfall at that status, indeed that same year, saw Dean just a week or so earlier smash into Mexico as a category 5 storm also supporting rare wind speeds in excess of 160mph and gusts which topped the stunning 200mph barrier as it made landfall. Not one but two LANDFALLING cat 5's is literally unheard of in this modern age. Yes, it's rare to support a category 5 storm in the first place, but even rarer to see one come ashore as it continues intensifying and it just so happened that those perfects ingredients which I talk about in the "Weather Talk" segment below where in place and sustained such two mighty storms onshore a week apart.
 
Igor may touch that cat 5 status for a time before weakening as it continues it's westward track and then takes a bentd more to the northwest. Why would it weaken if it's crossing ever warmer waters and the atmosphere appears to remain conducive?
 
Several things come into play which are also mentioned below, but a key is sustaining such power is tough to do so once these rare storms peak, I do believe the "peaking of intensity" with Igor remains ahead but once it peaks, then it will likely undergo an eyewall replacement cycle and may actually intensify to category 5 strength thanks to the storms reaction to what's it's naturally going to go through.. What's that mean? Well the storm wanting to undergo an eyewall replacement cycle may in fact force it to become stronger as it starts to undergo it's cycle of replacing the eye as the eye shrinks, pulls in those fierce winds that are spinning around the eye inwards, excellerating the air as it does so, perhaps making it's eye pin-like but collapsing in on itself!

OTHER TROPICAL NEWS
 
Karl Is Next in the Atlantic
AccuWeather News
 
Today's Weather across America
From AccuWeather
 
Quick-Hitting Thunderstorms in the Northeast Monday
By Alex Sosnowski, Expert Senior Meteorologist
 
Another Wildfire Ignites in Colorado
By Katie Storbeck, Meteorologist
 
Weather Talk
By Mark Vogan
 
Why is it tough for the Ocean and Atmosphere to Support Category 5 Hurricanes in the Atlantic?

Taking an In-Depth look at Maximum Potential Intensity

Projections in measuring the future power of a tropical cyclone is a science still in it's infancy but there are rules in which forecasters go by given the state of the playing field out there.

There are maps in which measure "MAXIMUM POTENTIAL INTENSITY" and certain years have sections of the Atlantic basin that see's higher MPI than other years, this year is higher given several factors which I will explain below. Other years the MPI is lower.. There are key areas of the Atlantic basin that "typically" has higher MPI than other areas.

THE STORM

In order for a storm to undergo either steady or rapid intensification, several factors must all come together at the same place at the same time, and that is extremely difficult to see happen, that's why in the Atlantic, it's rare to see a storm both rapidly intensify and or become a top-ranked category 5.

However, in order to see the Katrina's, Rita's, Wilma's, Ivan's, Isabel's, the actual maturity of the storm itself must then be looked at closely. 1) How well developed is the inner circulation i.e. the core.. the eye, the eyewall structure, the central dense overcast (CDO), is there a solid (thick), unborken ring of strong, self-generating thunderstorms (also known as hot towers) surrounding and making up the eye-wall?, is the overall circulation and air flowing uniformly around the system, is there good inflow at the surface and good outflow over top of the system where it releases excess energy out and away from the storm at the top, like an exhaust, remembering that a well formed, fully self driven hurricane, will recycle the kenetic energy it releases as outflow, as the air is forced overtop of the storm, then once outside the system's circulation, the high pressure that sits overtop of the storm will force the excess energy back to the ocean surface, where the storm will pick this back up, pulling it to it's core and then drawing up back up through the updraft columns where those strongest thunderstorms are racing around the center, regenerating air that was usable, then waste, and then transformed back usable energy, this re-cycling of air is repeated over and over again.

THE PERFECT SCENARIO THAT RARELY HAPPENS

High octane fuel that lies within a given area of ocean from surface to perhaps 250 to 300 feet down below the surface in which a warm current or even eddy flows (Gulf loop current or Gulf Stream), containing water temperatures above 85 degrees to depths of 250 feet or lower below the surface. A near perfect atmosphere above, say with no wind shear within a column spanning anywhere from 200 to 800 miles wide and upwards of 50,000 to 75,000 feet above the ocean surface. That same column which has a vertical thermal profile which supports temperatures at the surface and low-levels just above the ocean surface of 27-30C, plenty of heat and moisture which is vented off the very warm ocean into the low levels, compaired with an upper-level temperature of -70 to -85C, a vertical contrast which supports a very strong upward flow of air.. This would be considered a region supporting a high level of "Maximum Potential Intensity" if a storm was to move into this area.

LOOKING AT THE ATMOSPHERE

One must look at 1) SSP (Sea Surface Pressures), are they low enough for these systems to realistically drop their pressure further than it already is, 2) Is the overall atmosphere conducive for further intensification, i.e, the vertical profile of the atmosphere, is wind shear present, if so is it low enough to not hinder the storm's vertical structure of air flow? Is there a good vertical thermal profile in the columns of the atmosphere both containing the storm system and out ahead of it?, i.e temperature spread from the surface to the upper-levels, say from 27-30C at the surface to -70C or lower at the upper-levels..

So, if the pressures are uniformly low across a broad area of the tropical ocean, the air is plenty moist and warm, there is little to no wind shear across a broad area and indeed there is no dry air or other areas of low pressure nearby to inhibit potential intensification than there is no reason in which this type of atmosphere can't allow further growth of an already well organised and heatlhy storm system.

LOOKING AT THE OCEAN

When looking at the Atlantic Tropical Ocean Basin, there is a broad uniform area where water temperatures at the surface are 80F or 27C or warmer. Warm enough to support a tropical cyclone, but is it warmer enough to support intensification?

That uniform 80 degrees water at the "skin" of the ocean surface may only be at a depth of 50 feet, therefore, as a cyclone crosses over waters of 80 degrees which only supports that temperature of 80 down to 50 feet, then as the water is churned up, drawing deeper water upwards to the surface, then it may be just enough to support the cyclone's initial intensity or may even drop it's intensity as cooler waters below the 50 foot depth would perhaps lower the surface temperature from 80 to say 75 degrees....

This can be the case during the early season over the eastern Atlantic, nearer the African continent. That's why the so-called Cape Verde season, those long tracked storms that cross the entire-breadth of the tropical Atlantic only really kicks off in late August into September as waters aren't warm enough or deep enough, but once a near summer long heating of the ocean surface drives SST's to perhaps 83 degrees over the eastern basin, 85 over the central basin (where Igor is presently) and 86-88 degrees over the western basin do things really get going. Those cat 3s, 4s and 5s only form near the "peak of the season" when waters are closest to their peak...

What's important when looking at how strong a hurricane could potentially become can't be looked at by simply looking at what those SST's are, it could be over 85 degrees at the surface, but only for 50 feet down. If the "skin" temperature was the important factor and was say 85 degrees and covering much of the ocean surface in the tropics, then a much larger area of high percentage "maximum potential intensity" would then be given. However, it's temperature verses depth that counts as well as of course the state of the storm and it's atmosphere surrounding... yes, you didn't think it was as tough to get these kinds of ingredients infusing together did you?

Igor, is an example, and similar to both Isabel of 2003 and Ivan of 2004 where a storm literally "bombs out" over the open, central Atlantic. Waters are in the 85-87 degree range below and ahead of Igor and I believe they must stretch to depths lower than where the system would tap and churn colder waters, perhaps there's warm eddy's flowing and spinning under Igor, providing a constant feed of high octane fuel. The system is about as well organised and developed as it really can be, the atmosphere both within and surrounding the system is about as conductive as it could be also.. therefore the perfect scenario has and is unfolding, supporting Igor as a powerful category 4, 150mph hurricane.

What's more unusual about storms topping this intensity over the central Atlantic is that both Caribbean Sea and Gulf of Mexico supports warmer and deeper water than the Central Atlantic, however a net temperature of perhaps 1-2C warmer than normal may help spread that higher percentage of MPI furtherout into the tropical Atlantic, spreading a heat content more comparable to the Caribbean Sea eastwards and into the path of Earl and Igor of 2010, perhaps even in the form of an eddy which breaks off from the main channel within the Caribbean and Gulf.

Theoretically, you'll never find 100% maximum intensity, even with Katrina and Rita of 2005 topping 175mph sustained winds in the Central Gulf of Mexico (reasoning: perfect atmosphere, circulation maturity and extremely warm waters of 90 degrees,27s all about whether Igor will ow the surface), even then it was probably around 70 to 80% MPI, given the ingredients in place.

Where Isabel topped cat 5 intensity over the western Atlantic, not too far west of Igor, the MPI was probably around 70 to 75% and I would say Igor is around 65 to 70% given the ingredients, perhaps nearing 70% if he can reach cat 5 status before an eye-wall replacement cycle commences.. also remember, it's tough for the atmosphere to support such power and these systems tend to peak quick and then they regenerate their own structure at the center where the eye becomes obsorbed by the surrounding circulation in which it basically swallows it up, often as this is occuring, you can often see a new eye already forming on the outer edge of the collapsing inner ring of the old eye...

So, the western Atlantic where waters are geberally warmer and deeper, have higher MPI percentages than over the central and eastern tropical basin. Some years the percentage in the central and eastern basin can be higher, like this year for example where waters are 1 to 2 degrees above normal, for the Caribbean and Gulf, they too can have a greater net energy potential than other years, in 2005 the potential was basically about as high as it could go in reality (around 70 to 80% MPI) as the uniform surface of the Gulf was 2-4 degrees above normal, plus the flow of the loop current was strong and right in the path of incoming hurricanes, the combo allowed Katrina and Rita to blow into top-ranked "scary" storms.. As for the western Caribbean Sea, that is basically the prime area of MPI in any given year but in 2005 Wilma was the perfect example as to just how warm and deep those waters are and how they react to a well developed storm.. Wilma probably topped 85 to 90% MPI given waters are warmest than anywhere else in the Atlantic basin(probably over 90 degrees and to depths over 450 to 500 feet below the surface).



What's Reaching Today's Blogs?
 
Hurricane Igor Gives Second Shot At Category 5
Jesse Ferrell, AccuWeather

Today's US Extremes
Courtesy of AccuWeather

High: 111 degrees at Death Valley, CA
Low: 19 degrees at Bodie State Park, CA
Today's Extremes here at my house
 
High: 61 degrees
Low: 54 degrees

Thanks for reading.
-Mark