Monday, June 8, 2015

Another Rare June Tropical Cyclone Remnant Visit

The passage of tropical cyclone (TC) remnants across the southwest U.S. is rare, but not unprecedented in June.  As illustrated by Ritchie et al. (2011),  rainfall events associated with TC remnants are most common over the southwest U.S. in September.  Action in June is more limited.  During the 1992–2005 period examined by Ritchie et al. (2011), there were only 2 rainfall events associated with TC remnants in June.

Number of eastern Pacific tropical cyclones, number of tropical cyclone remnants that brought rain to the southwest U.S., and number of tropical cyclone remnants that did not bring rain to the southwest but had other impacts.  Study period 1992–2005.  Source: Ritchie et al. (2011)
We've already had one this year associated with TC Andres, and now we'll have another associated with TC Blanca.  Blanca was a category 4 hurricane, but as of this morning had weakened to a tropical storm centered near the Isla Santa Margarita off the west coast of the Baja Peninsula.  High clouds in advance of Blanca were already streaming into southern Arizona.

As can be seen in the contours above, Blanca is accompanied by a slug of high integrated water vapor (a.k.a. precipitable water) and preceded by a surge of high integrated water vapor up the Gulf of California.  This moisture is expected to push into southern California and Arizona today and stream into southern Utah late tomorrow.  At the same time, moisture from the midlatitude Pacific also pushes into the Intermountain region from the west.

Thus, although we're in a bit of a break today and tomorrow, with just some isolated mountain showers and thunderstorms, the action should be on the increase after Tuesday with a good chance of showers and thunderstorms statewide on Wednesday and Thursday.

After nearly turning on my sprinklers in April, I still haven't run them and if we can get more rain midweek, I'll likely make it to at least the middle of the month.


  1. Dr Jim, We haven't watered the lawn yet, our best "start was 7-1 a couple of years back, but we are down with brown.

  2. I like the graph. It looks like July might possibly have the lowest probability of impacts on the U.S. for the eastern Pacific tropical systems that do form, due to the fact that there is rarely any trough activity off the CA coast to bring them north that time of the year. In early June, even though hurricanes are uncommon, the probability of having a closed low off the CA coast (as in this case) is at least a little better. Obviously September combines the highest number of tropical systems with the most favorable mid-latitude patterns.

  3. Are TC remnants what causes the spring/summer monsoons or are they different? Hoping for some good strong high pressure setup as we have a soaring contest scheduled for late June and early July in Nephi.

    1. The TC remnants don't cause the monsoon, but they contribute to some degree to the total monsoon precipitation.