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Subject: G8) Does an active June and July mean the rest of
the season will be busy too?
Yes and No. The vast majority of Atlantic activity takes place
during August-September-October, the climatological peak months
of the hurricane season. The overall number of named storms
(hurricanes) occurring in June and July (JJ) correlates at an
insignificant r = +0.13 (+0.02) versus the whole season activity.
In fact, there is a slight negative relationship between early
season storms (hurricanes) versus late season - August through
November - r = -0.28 (-0.35). Thus, the overall early season
activity, be it very active or quite calm, has little bearing on
the season as a whole. These correlations are based on the years
1944-1994.
However, as shown in (Goldenberg 2000),
if one looks only at the June-July Atlantic tropical storms and
hurricanes occurring south of 22°N and east of 77°W (the
eastern portion of the Main Development Region [MDR] for Atlantic
hurricanes), there is a strong association with activity for the
remainder of the year. According to teh data from 1944-1999,
total overall Atlantic activity for years that had a tropical
storm or hurricane form in this region during JJ have been at
least average and often times above average. So it could be said
that a JJ storm in this region is pretty much a "sufficient" (though
not "necessary") condition for a year to produce at least average
activity. (I.e., Not all years with average to above-average
total overall activity have had a JJ storm in that region, but
almost all years with that type of JJ storm produce average to
above-average activity.) The formation of a storm in this region
during June-July is taken into account when the August updates
for the
Bill Gray and
NOAA seasonal forecasts are issued.
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