27 October 2005

Beta forms in southwestern Caribbean...

The area of disturbed weather I've been mentioning all week was upgraded 
to TD26 at 03Z today, then further upgraded to TS Beta at 09Z today, 
making it the 23rd named storm of the season.

The satellite presentation is classic, and I see no reason why it would 
not continue to intensify at a respectable rate.  Microwave imagery at 
14Z revealed a compact and intense core under the CDO, and there are two 
major bands on either side of the center.  Shear is minimal, and SSTs 
are plenty warm, but the oceanic heat content drops off dramatically 
just to Beta's north, indicative of a shallow warm layer.


The official forecast takes Beta up to a CAT2 hurricane before drifting 
into the northern Nicaragua coast in several days.  The rainfall from a 
slow-moving tropical cyclone near mountainous terrain can be devastating.  
There is a distinct possibility that it will drift far enough north to 
miss Central America and head up toward the Yucatan or Cuba.

There are two other tropical waves out there that I've been discussing... 
one that exited Africa on Oct 19 and one that exited on Oct 23.  They 
are currently located at roughly 62W and 40W, respectively.  Both have 
been persistent, easily-tracked waves, but both have been suppressed by 
strong vertical wind shear.  However, conditions are gradually improving 
for the western one, which is just now crossing the Lesser Antilles.  
This has the potential to become TD27 or Gamma in the coming week.  

The NTC (Net Tropical Cyclone activity) is up to 236% as of 15Z today.  
This index takes into account the numbers of named storms, hurricanes, 
and intense hurricanes, as well as their respective longevities, and 
compares them to a climatological values of each.  An NTC of 100% would 
mean the June 1 - November 30 hurricane season was "average".

Today is the 300th day of the year, and "normally" we'd be talking about 
the 10th named storm, not the 23rd!  One of the principal drivers of 
activity in the Atlantic is the "Atlantic Multidecadal Oscillation".  
This is related to the basin-wide ocean circulation whose speed 
partially controls the SSTs and heat content.  Since 1995, this index 
has been positive, then was negative between 1970-1994, but before that, 
was mostly positive from the mid 1920s to late 1960s.  So, if history is 
a teacher, we should be in for a long period of this enhanced activity 
before the AMO swings back to the negative phase -- perhaps another 
20-30 years?  The problem is, there is a lot more life and property in 
harm's way during this active era compared to the last one 50-80 years 

Please visit my tropical Atlantic headquarters.

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