|
|
|
National Weather Service Tucson Arizona
| |
Remainder
of the Monsoon outlook & |
| |
an
early look at 2009-10 winter season |
| |
for
southeast Arizona |
| |
updated on August 24th |
| |
|
| |
The latest forecast
from the Climate Prediction
Center has not changed as we head into the last stage of
the 2009 monsoon. The official forecast calls for equal chances
that rainfall will be above or below average through the end of
the monsoon season on September 30. There remains an elevated chance
that temperatures will be above average.
|
| |
|
| |
Since
mid July, the monsoon has been significantly impacted by a developing
El
Niño. As it has continued to strengthen, the jet stream
has become stronger than usual, and has had a tendency to buckle into
unusually early upper level troughs along or off the west coast. This
has suppressed the monsoon high south and east of Arizona. As was
feared that this would happen back in May when the El
Niño started to develop, thunderstorm activity has
been greatly suppressed since mid July over all but the far southeast
corner of the state, along with hotter than average temperatures due
to the absence of cooling rains. |
| |
|
| |
While
this overall trend is likely to continue, the forecast purposely does
not call for below average rainfall in September or in the September-November
period. With a mean cool season trough already trying to establish
itself near the west coast, there will be a tendency for low pressure
systems to move off the north Pacific and across the southwestern
United States earlier than usual. Depending on where these individual
systems track, they could tap monsoon moisture, which will remain
quite plentiful over Mexico, and pull it north into Arizona rapidly.
Thus while lengthy hot and dry spells are likely to continue for the
rest of the monsoon, they may be punctuated by an unusually wet episode
or two in September and October. |
| |
|
| |
Another
key factor is that water temperatures off the west coast of Mexico
have been tending 2 to 4° F degrees warmer than average this summer,
with an area of water temperatures above 80° F expanding usually
far north along the west coast of Baja California. This should lead
to an increase in tropical cyclone activity over the eastern Pacific,
with these systems more likely to survive if they move northwest along
the southwest Baja coast. This in turn increases the chance that the
mean west coast trough will pull remnant tropical moisture north and
recharge the monsoon. In the worst case, it could even steer a weakening
tropical depression or tropical storm into the region, bringing both
heavy rain and high winds. Atmospheric conditions have to be just
right for this interaction to occur, but the strengthening El Niño
increases the chance for these atmospheric conditions to align through
early October. |
| |
|
| |
| September |
December
2009 to February 2010 |
| precipitation
forecast |
precipitation forecast |
 |
 |
| Click
image to enlarge |
Click
image to enlarge |
|
| |
|
| |
|
|
| |
|
|
|
Webmaster
US Dept of Commerce
National Oceanic and Atmospheric Administration
National Weather Service
Tucson Weather Forecast Office
520 North Park Ave, Suite 304
Tucson, AZ 85719
Tel: (520) 670-6526
|
Disclaimer
Information Quality
Credits
Glossary |
Privacy Policy
Freedom of Information Act
About Us
Career Opportunities
|
|
|
www.weather.gov 
