From: landsea@typhoon.atmos.colostate.edu (Chris Landsea)
Newsgroups: sci.geo.meteorology
Subject: Status of hurricane season and Gray's forecast
Keywords: hurricanes, forecasting
Date: 2 Sep 92 15:54:48 GMT
Organization: Colorado State University -- Atmos Sci


Since the Atlantic hurricane season is officially half over now (but in
actuality September 10 or so is usually the midpoint in activity), I 
thought a quick discussion on how that Dr. Gray and his forecast are
going so far.

We've had just one tropical cyclone of tropical storm strength or greater -
that being of course:  Andrew (which just happened to be one of the worst).
In an average year (but what year *is* average), we would have about 4
named storms, 1 or 2 being hurricanes.  Fortunately, overall the season
has been quieter than normal (the US certainly doesn't need any more
storms this year); but the question is what will September and October
bring?

If Gray's forecast is to verify, there needs to be 7 more named storms, 3
of which becoming hurricanes, none of which becoming another Category 3,4,
or 5 hurricane.  This is certainly possible - these are likely factors:

- El Nino no more:  The Nino 3 region (off the west coast of South 
                    America) showed a 0.1 deg C warm anomaly, or near
                    normal conditions.  El Nino will certainly have no
                    effect in late September or October.  More storms
                    possible.

- West Sahel rain:  June and July were below normal rain for that region
                    indicating a weaker hurricane season.  August was
                    closer to normal, but prospect are for overall weaker
                    easterly waves and a weaker 200 mb African easterly
                    jet:  Less storms possible.

- QBO phase:        The phase of the stratospheric QBO (quasi-biennial
                    oscillation) is shifting from easterly to westerly
                    at 50 mb during September and October:  neutral effect.

- Beven's Pac-Man   The semi-permanent mid Atlantic trough, or TUTT, appears
  Trough (it eats   to be strong this year, with big westerly winds 
  storms)           screaming across the Caribbean's upper troposphere.  If
                    it continues, less storms possible.

- Pinatubo effect?  If, as many have speculated, that the cool winter the US
                    is having, is induced by more equatorward than normal
                    jet stream from a higher albedo reducing solar to the
                    mid-lats, then this may cause the hurricane season to
                    end sooner.  Tropical cyclones need a minimum of shear
                    and in the Atlantic tradewind environment, this means
                    easterlies aloft.  Possible effect:  less storms
                    (On this I do have my doubts though, most of Europe has
                    had a warmer than normal summer...why Pinatubo for us (US)
                    and not them?)

Overall, it looks like Gray's forecast will verify well.  What follows are
his forecast numbers and the count to date.  I will repost when (if?) we
get more storms.  Also, if you would like to get the following on your
own, type:   finger forecast@typhoon.atmos.colostate.edu
       OR
             finger forecast@129.82.107.24

STATUS OF GRAY'S ATLANTIC           Long | Nov 26 | Jun 05 | Aug 05 |
SEASONAL HURRICANE FORECAST         Term |  1991  |  1992  |  1992  |
FOR 1992                            Mean |  Fcst. |  Fcst. |  Fcst. | Current
=============================================================================
Named Storms                         9.3 |    8   |    8   |    8   |    1 
Named Storm Days                    46.7 |   35   |   35   |   35   |   9.5 
Hurricanes                           5.8 |    4   |    4   |    4   |    1 
Hurricane Days                      23.7 |   15   |   15   |   15   |   4.2 
Major Hurricanes (Category 3-4-5)    2.5 |    1   |    1   |    1   |    1 
Major Hurricane Days                 5.8 |  2.0   |  2.0   |  2.0   |   3.5 
Hurricane Destruction Potential     73.8 |   35   |   35   |   35   |  21.5  

Chris

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Chris Landsea                          Voice:  (303) 491-8605
Department of Atmospheric Science      Fax:    (303) 491-8449
Colorado State University              Internet:  landsea@typhoon.atmos.
Fort Collins, CO   80523                          colostate.edu
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Newsgroups: sci.geo.meteorology