652 
FXUS65 KTWC 101557
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
855 AM MST Wed Oct 10 2018

.SYNOPSIS...Dry with below average temperatures into Thursday. 
Increasing moisture from tropical system Sergio and a Pacific 
storm system will bring showers and thunderstorms to much of the 
region Thursday night into early next week.

&&

.DISCUSSION...Expecting another nice day today across Southeast 
Arizona with high temperatures 4 to 7 degrees below average for mid-
October. Things will change over the next 24-48 hours though, as 
Tropical Storm Sergio makes a beeline for the Baja California Sur. 
The latest forecast from the NHC (8 AM PDT this morning) has the 
center located 930 mi WSW of the southern tip of Baja California 
moving toward the northeast at 11 kts. It is expected to make 
landfall on the Baja sometime early Friday morning, but we should 
start to feel the effects of increased moisture a bit sooner than 
that. With the current NHC forecast tracking the remnant low 
pressure center southeast of here, lingering moisture will then be 
worked on by an upper low progged to settle off the southwest coast 
of California this weekend and early next week. This could make for 
several days with periods of cool, cloudy and showery weather. More 
info on this with the afternoon package. For now, the near-term 
forecast looks good and there are no updates. Please see the 
remaining sections for further information.

&&

.AVIATION...Valid through 11/18Z.
SKC for most of the day today, then FEW-SCT clouds 5-10k ft AGL late 
this afternoon through the end of the forecast period. SFC wind 
generally less than 10 kts this morning becoming SWLY at 8-12 kts 
this afternoon. SLY to SELY winds then occur overnight into Thursday 
morning at 10-15 kts. Aviation discussion not updated for TAF 
amendments.

&&

.FIRE WEATHER...Dry conditions are expected today with 
temperatures several degrees below normal. Increasing moisture 
associated with tropical system Sergio is expected to result in 
areas of showers and thunderstorms as early as Thursday afternoon 
and continuing through Friday night, with an emphasis on locations 
southeast of Tucson through Friday. A secondary weather system will 
keep unsettled weather continuing through the weekend and early next 
week with isolated to scattered showers and thunderstorms each day. 
20-foot winds will be terrain driven and generally less than 15 mph 
through the weekend.

&&

.PREV DISCUSSION...A noteworthy change in the forecast was made on 
the morning package. The track of tropical system Sergio remained 
the same with the bulk of the moisture moving into northern Mexico 
and extreme southeast Arizona Thursday night and Friday. Remnants of 
Sergio will result in widespread moderate rainfall across the area 
with some locally heavy rainfall possible south and southeast of 
Tucson. The big change in the forecast deals with the low pressure 
system dropping south along the California coast behind remnants of 
Sergio. Latest models appeared to have a better handle on the 
evolution of this upper low as in tracks into southern California/ 
northern Baja by Sunday. This upper low will interact with the 
tropical moisture brought into the region with Sergio. Thus, it 
appears that rain chances will remain good over the weekend into 
early next week.  

&&

.TWC WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson