18 July 2003

Danny nearly a hurricane...

As forecast, the weak shear over Danny has allowed him to intensify, and
the satellite presentation is impressive, with symmetric outflow and
well-defined bands.  However, the convection is not very centralized. 
The cloud tops temps aren't very cold either, but keep in mind that the
storm is at nearly 40N, so the tropopause height isn't as high (cold) as
it is in the deep tropics.  And once again, I'll draw your attention to
another difference one must consider when watching a tropical cyclone so
far north... the central pressure is 1009mb, and he's nearly a
hurricane.  In the deep tropics, that same pressure would barely be a

At 15Z today, TS Danny was located at 38.7N 54.3W and tracking NE at
14kts.  Maximum sustained winds are 60kts with a MSLP of 1009mb.  The
forecast is for gradual weakening, but any slight spike in intensity
would bring him to hurricane intensity (65kts+).  Although the shear is
still favorable, the SSTs are dropping off now that he's crossed the
Gulf Stream axis... presently 25.5C and decreasing as he heads NE.  As
I've mentioned before, his track has been governed by the Bermuda High
sitting over the north central Atlantic (centered at about 35N 40W). 
Flow around the High is clockwise.  Most models keep a traceable system
(maybe not quite a tropical cyclone) for several days, eventually
wrapping (ex-)Danny back around into the warmer part of the basin, so
we'll have to keep an eye on this vortex for a while perhaps.

Ironically, the last time we had two hurricanes during July was 1997,
and they were Bill and Danny.  So maybe this cycle's Danny will also
become a second July hurricane??

Two tropical waves in the deep tropics seem to be ingesting very dry air
from the Saharan Air Layer (SAL).  This is a plume of silicate-laden air
from the African desert that blows westward across the tropical
Atlantic, sometimes reaching the central Caribbean.  It varies in
intensity, but apparently is unfavorable for convective development. 
shows a GOES-12 visible image from this morning at 1145Z.  Note the
milky color streaming across the deep tropics from Africa.  You're not
seeing DRY air, but actually the silicates and sand aerosols from the
Sahara (the air is dry, but you couldn't prove that with visible imagery

Please visit my tropical Atlantic headquarters.

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