| cieldumort |
| (Moderator) |
| Sun Oct 31 2010 09:46 PM |
|
Re: Hurricane Tomas now Category 2
|
Quote:
The last two advisories have shown weakening. What changed from the further stregthening forecast?
That's a very good question!
The NHC does a pretty good job explaining it during the 5PM Discussion:
Quote:
SOME ADDITIONAL WEAKENING SEEMS LIKELY DURING THE NEXT DAY OR TWO AS
SOUTHWESTERLY SHEAR OF 20-25 KT AND SOME MID-LEVEL DRY AIR CONTINUE
TO IMPACT THE CYCLONE. THE OFFICIAL FORECAST FOLLOWS THE TREND IN
THE GUIDANCE AND IS ONCE AGAIN ADJUSTED DOWNWARD...BRINGING TOMAS
BELOW HURRICANE STRENGTH WITHIN THE NEXT 12 HOURS. BEYOND A COUPLE
OF DAYS...THE SHEAR IS EXPECTED TO LESSEN WHILE TOMAS REMAINS OVER
FAVORABLE OCEANIC CONDITIONS. ALL OF THE INTENSITY MODELS RESPOND
AND SHOW THE SYSTEM INTENSIFYING IN THE 3 TO 5 DAY RANGE...AND THE
OFFICIAL FORECAST FOLLOWS SUIT AND IS AT THE HIGH END OF THE
GUIDANCE THROUGHOUT THE FORECAST PERIOD.
(LINK)
In general, tropical cyclones benefit from air currents that do not disturb their cyclonic flow, and also that do not interrupt any anticyclonic flow that exists above them. The shear that the NHC speaks of is currently working against Tomas in this regard, as well as allowing some drier air to penetrate the system, which is further damaging to tropical cyclones.
Hope that helps!