Why next week could get interesting

Published: Sep. 3, 2016 at 12:19 AM MST|Updated: Mar. 2, 2018 at 4:11 PM MST
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You've heard us talk about Hermine, Madeline and Lester this week, but now we are turning our attention to what's happening in the east Pacific about 1,400 miles south of Arizona.

The National Hurricane Center has a 70% probability of this area of disorganized thunderstorms becoming a tropical depression over the next 48 hours.

Some computer models take the moisture from this tropical system up the western coast of Mexico, and eventually through the Gulf of California by early next week.  If this happens, it's likely Arizona would see a surge of deep tropical moisture, which could drop a lot of rain over a few days.

image: Wright Weather 

Each individual line in the image above represents the track from a computer model.  The consensus is almost a straight shot northwest to Baja California.

image: Tucson News Now

Above is our in-house RPM computer model showing where rain could be by Monday.

There are several key features that we'll need to watch over the next week.  Number one is the positioning of the jet stream over the western U.S. If the jet shifts to the east, it could squash the moisture south and hinder further tropical development.  If it stays just to the west of Arizona, it could trigger a tropical moisture surge.

image: WSI - 12z GFS computer model

Now we move forward to Wednesday morning, which is what the image above is showing.  This computer model doesn't show much development of the tropical cyclone, but does still show a more minor surge of moisture that would trigger monsoon storms.

image: WSI - ECMWF computer model

Above is the same time Wednesday morning, but this is the European computer model.  The Euro shows a more defined (likely a tropical storm) tropical cyclone.  This model brings in more widespread and heavier rain Wednesday through Friday next week.

The Bottom Line:

Ultimately the placement of the, by then, extratropical low (Hermine) off the northeast coast will influence the placement of high pressure over the southeast, which could slow the eastward progression of the jet stream over the western United States.  Basically, one ripple could change everything.

We don't know what a tropical cyclone will do before it even develops, so we are going to need more time to fine-tune and adjust the forecast as we get closer.  For now, we've included and indicated a chance of rain by late Tuesday through Friday; with the best chances of heavy rain being Wednesday and Thursday.

This is where we don't want to hype up a storm and throw a high-percentage chance of rain right away.  The track of this tropical system, that again, has not developed yet, could easily change within a couple of new-model runs.

We will keep you updated here, on KOLD, and on our Tucson News Now weather app.

If the cyclone becomes a tropical storm and gets a name, it would become Tropical Storm Newton.

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