The newest 6-10 and 8-14 day precipitation outlooks show wet conditions continuing. We should be dry today and Friday. There is a chance for showers over the weekend and into early next week. Sometime in the second half of next week, tropical storm, soon hurricane, Odile will deliver more moisture to Arizona.
We will be entering another wet period this weekend. It will last through the first half of next week. The moisture is a result of an Eastern Pacific hurricane named Norbert. Norbert is tracking up the west coast of Baja Mexico. This morning, Norbert is west of the southern tip of the Baja Peninsula. Below is an animated GIF of the GFS Model for the next 4 days. It shows 24-hour predicted precipitation in daily intervals. You can see Norbert in the animation. He’s bringing plenty of moisture to Arizona.
With a fire at this time of year, it’s natural to look at the calendar and think about how long until monsoon season, and will it be a good one. The Climate Prediction Center has Flagstaff inside the above normal region for the June-August and the July-September 3-month precipitation outlooks(see below). The current June outlook has us at even chances for normal precipitation.
A particularly interesting part of the monsoon season is Eastern Pacific hurricanes and tropical storms. These can bring exceptional moisture to Arizona. Hurricane season for the Eastern Pacific start on May 15th. Hurricanes do not usually form in May in this region, but they can. If they do form, they usually wander around the coast of Southern Mexico or drift straight out to the west. This year, we have our first storm, Hurricane Amanda. The computer models show Amanda moving up the West Coast and bringing moisture to Arizona by late in the week. It is still 5-7 days out, but it could at least help keep our temperatures lower and out humidity higher for a while.
One last note: The Climate Prediction Center issued an El Nino watch. The current outlooks show a strengthening El Nino that could be quite strong for next year. My current question is whether this could derail our monsoon season.
A recent question I have heard frequently is “Since the monsoon season was so wet, does that mean we will have a snowy winter.” A few years ago, the National Weather Service in Flagstaff included a slide in their winter outlook presentation that showed no clear link between summer and winter precipitation. In general, given the mechanisms for out summer and winter weather patterns, they shouldn’t be linked.
I cover the summer monsoon pattern in detail on this link: Summer Monsoon Mechanics. In this season, a thermal low develops over the deep southwestern United States. Also, a high pressure system forms over the middle of the country. The anticyclonic and cyclonic flows around these systems drive flow from the south and southeast. This flow draws up moisture from the Gulf of Mexico and the west coast of Mexico. Since the jet stream remains far to the north, these systems can be fairly stable. The big disruption of the monsoon pattern usually comes from hurricanes in the Gulf of Mexico. Interestingly, this year’s hurricane season has been anemic with only 2 hurricanes forming in the Atlantic. The other very wet year, 1986, saw a season total of 4 hurricanes.
In our winter pattern, the jet stream drops farther to the south and drives strong storms from west to east. In winters with a El Nino in the equatorial Pacific, the jet stream can split in two. One jet remains to the south and carries storms across the southern tier of states. The moisture reservoirs for the winter pattern end up being different from the summer. One supply area is from a large area near the Hawaiian Islands. When this water is warmer than normal it can be a powerful moisture supply. This happened in December of 2010. The other moisture supply can be from the equatorial Pacific in El Nino years. Occasionally, in very cold years, the Pacific Ocean off the west coast of Mexico can be warmer than normal and provide limited moisture.