Hurricanes and tropical storms can severely alter the monsoonal flow pattern, as previously mentioned. Here is a graphic of this years hurricanes/tropical storms. Early in the season, Hurricane Alex (6-25-2010 to 7-2-2010) and tropical depression #2 (7-8-2010) both stalled the development of our monsoon pattern.
These both corresponded to dips in our dewpoint as far north as Flagstaff during the same time periods. You’ll notice the earlier drop, around June 21. That was due to storm systems moving by to the north and providing us with strong southwest breezes. The current trend to normal dewpoint temperatures is related to fluctuations in the high and low pressure complex that drives the monsoon.
Why bring this up today? NOAA is revising their hurricane forecast for the season today. The expectation is that they will revise it downward. The season to date has been roughly average. They had forecasted an aggressive sesaon. However, the Caribbean Sea is fairly warm warm compared to average. So, we will see.
But, if you think back to the severe 2005 season, Hurricanes Katrina and Rita devastated the Gulf Coast and abruptly ended a rather good monsoon season. Hurricanes have a strong effect on our monsoon.