Dry
Summer to Continue for Kwajalein
by
Vanessa Richard, RTS Meteorologist
2
August 2007
The
ENSO-neutral conditions currently occurring are expected to persist
through the remainder of the year. Therefore, Kwajalein Atoll can
expect average to below-average rainfall that may exhibit high
month-to-month variability, a low risk for tropical cyclone activity,
and a slight chance that doldrums or west winds will last for any
length of time as the northeasterly trade winds will dominate.
ENSO
is an acronym for the El Niño-Southern Oscillation, a
phenomenon in the equatorial Pacific Ocean that can affect the
climate cycle around the globe. When the ENSO cycle is positive, it
is referred to as an El Niño event, and a negative ENSO is
also known as a La Niña event. There are signals that point
to which one of these phenomena may be occurring, such as sea surface
temperatures, wind speeds and general cloudiness across the
equatorial Pacific. Roughly speaking and in its simplest form, an El
Niño event is characterized by warmer than normal sea surface
temperatures in the eastern tropical Pacific. During El Niño
events, the Marshall Islands typically receives above-average
rainfall and an increased risk of tropical cyclones. A La Niña
event is essentially the opposite. There is no regular variability
to ENSO, and it is consequently difficult to predict. However,
because the impacts can be great on a global scale, ENSO shifts are
closely monitored.
After
last year’s El Niño event and the expected transition to
more La Niña type conditions, ENSO-neutral conditions have
currently been exhibited over most of the tropical Pacific.
Observations include average sea surface temperatures, stronger than
normal trade winds in the west-central Pacific, and suppressed
cloudiness east of the date line.
Zooming
in closer to home, current weather conditions on Kwajalein also
correlate with ENSO-neutral conditions. As many have observed, the
doldrums were late to arrive this summer as the deeper trade winds
persisted longer than usual. In fact the area has seen some
significant trade wind bursts over the past couple of months with
gusts to 29 knots, which is quite atypical for this time of year. So
far this year, Kwajalein has received rainfall totals 75% of normal,
coming up approximately 12 inches short at the beginning of August.
July was actually headed for a record low precipitation total up
until the last week of the month when over 50% of July’s rainfall
was received. The record low for July is 3.53” (1984) and
Kwajalein had received only 2.73” by the 25th.
By the
end of the month, the rainfall total settled out at 5.74”, which is
only 56% of normal July rainfall (10.24”). The last week of July
demonstrated the high variability in rainfall that is also
characteristic of ENSO-neutral conditions.
The Climate Prediction Center has stated that these conditions are expected to continue, as nearly all of the latest climate forecast models predict either a continued ENSO-neutral state or a slow transition to La Niña for the remainder of the year. Therefore most of the northern Marshall Islands can expect to continue to receive average to below-average rainfall. The risk for tropical cyclone activity in our region is below normal as well. While experts at the Pacific ENSO Applications Center in Hawaii recognize this, they have noted the possibility of remnants of eastern or central Pacific tropical cyclones moving into the western Pacific with a track somewhere between Kwajalein and Wake Island. This potential for significant rainfall is only expected through October - the virtual end of the cyclone season. Most of the tropical cyclone activity west of the date line will be relegated to western Micronesia (specifically Chuuk and westward). The seasonal monsoon trough that can bring wet weather into the Marshall Islands in the summertime will also remain influential only over western Micronesia and is not expected to reach the area, nor will the major west wind events that accompany it. The doldrums will continue to remain elusive for the remainder of the summer as well.