Potential factors for Monsoon 2017

One month away from the official start of Monsoon in Southern Arizona. Will the Summer storm season be a boom or bust? Here’s three things that may influence Monsoon 2017.

1: El Nino or not?

Basically, it’s a coin flip whether waters in the Eastern Pacific Ocean will be normal or slightly warmer. NOAA’s latest El Nino blog points out while sea surface temperatures (SST’s) are sharply warmer than average off Peru & Ecuador, it doesn’t guarantee the rest of the Eastern Pacific warms up as well.

So let’s say a weak El Nino pops up during the Monsoon. Out of the 18 recorded El Nino events during the Monsoon, 10 have recorded below average rainfall in Tucson. Only 3 of those Summer storm seasons saw above average rainfall.

2: The Eastern Pacific hurricane season

Tropical storm & hurricane development in the Eastern Pacific will be largely based on the previously mentioned El Nino. Warmer than normal waters can lead to an active season, increasing Southern Arizona’s odds for occasional boosts of moisture.

According to the National Hurricane Center, an average Eastern Pacific hurricane season breaks down like this:

  • 15 names storms
  • 8 hurricanes
  • 4 hurricanes reaching major status (Category 3+)

For what it’s worth, we’re already one named storm into the 2017 Eastern Pacific season. Adrian formed in early May, becoming the earliest tropical storm on record for the Eastern Pacific. In case you’re wondering…

3: Drought & the Monsoon high

We talk so often about the Four Corners High. That’s the sweet spot to get Monsoon storms to fire up in the Sonoran Desert. However, recent research has shown high pressure likes to settle into areas which were dry during the Winter & Spring. As of May 9th, a good chunk of the Southern Arizona was under moderate drought.

If high pressure sets up in these areas, it could shunt moisture south of the border & leave Southern Arizona with below normal Monsoon rainfall. Not a hard & fast rule, but a scenario that can’t be entirely ruled out.

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