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Monthly Archive

Southwest Climate Outlook Tropical Storm Tracker - October 2018

Monday, October 22, 2018

Atlantic hurricanes Florence and Michael have understandably been the focus of attention this year, but as discussed on page 1, 2018 has been an extremely active year for tropical storms in the eastern North Pacific. While most of the storms expended most or all of their energy over the Pacific, a few had notable impacts on the Southwest.

In mid-June, Tropical Storm Bud caused widespread precipitation across the Southwest just as the monsoon began, kickstarting cumulative monsoon precipitation totals, even as some argued it should not be included as part of the monsoon* (Fig. 1). In September, Tropical depression Nineteen-E brought widespread precipitation to the Southwest (Fig. 2) and was a major contributor to that month’s above-normal precipitation (see Fig. 5 on the Maps & Images page). October has seen two events (thus far) of notably different character. Tropical Storm Rosa brought intense precipitation to the borderlands region of Arizona and up to Phoenix (Fig. 3) at the beginning of the month, resulting in severe flooding in both regions, and one week later, Tropical Storm Sergio brought more widespread but less-intense precipitation to southern Arizona and parts of New Mexico (Fig. 4).

With an official end to the season not until Nov. 30, it remains to be seen how many more tropical storms might bring additional rainfall to the Southwest this fall.

Figures 1-4 - CLIMAS: Climate Assessment for the Southwest -


Southwest Climate Outlook El Niño Tracker - October 2018

Friday, October 19, 2018

Oceanic and atmospheric conditions are still within the range of ENSO-neutral (Figs. 1-2), but rising sea-surface temperatures (SSTs) and shifting atmospheric conditions are reflected in recent forecasts, which call for an El Niño event forming by the end of 2018 and lasting through the winter. On Oct. 11, the Japanese Meteorological Agency (JMA) identified continued ENSO-neutral conditions, but based on weakening easterlies and warming SSTs forecast a 70-percent chance of El Niño developing this fall. Similarly, on Oct. 9, weakening trade winds and warming oceanic temperatures were the basis for the Australian Bureau of Meteorology to elevate its ENSO Outlook to “El Niño Alert,” with a 70-percent chance of its formation in 2018—three times the normal likelihood. On Oct. 11, the NOAA Climate Prediction Center (CPC) continued its El Niño watch, identifying neutral conditions at present but with a 70- to 75-percent chance of an El Niño event developing this winter. On Oct. 11, the International Research Institute (IRI) issued an ENSO Quick Look, which observed neutral conditions in the oceans and atmosphere now but with trends towards El Niño conditions in oceanic and atmospheric indicators. IRI suggests a nearly 75-percent chance of an El Niño event by the end of 2018 (Fig. 3). The North American Multi-Model Ensemble (NMME) stabilized over the past few months but continues to point toward a weak-to-borderline moderate El Niño by the end of the year (Fig. 4).

Summary: Despite persistent ENSO-neutral conditions this summer and early fall, outlooks and forecasts indicate the likely formation of an El Niño event before the year ends. These forecasts are informed by long-term climatological patterns and recent trends towards warming SSTs and shifting atmospheric conditions. There is effectively no chance of a La Niña event forming this winter, but ENSO-neutral conditions remain a possibility, albeit increasingly unlikely. The recent warming in SSTs and shifts in atmospheric circulation have kindled discussion about the possible intensity–rather than merely the existence–of this El Niño event. Cool-season precipitation totals (Oct – Mar) in the Southwest during previous El Nino events reveal considerable variability under weak events, including some drier-than-average seasonal totals. However, under moderate-intensity events, drier-than-average cool seasons have been rare. While it is too early to even call this an El Niño year with 100 percent certainty, much less predict its eventual intensity, we wait with great anticipation anything that might increase our chances of more winter rain. The sample size is small, but an El Niño of at least moderate intensity has been one of the more surefire pathways to a wetter-than-average Southwest winter (setting aside 2016 as the obvious outlier).

Online Resources

  • Figure 1 - Australian Bureau of Meteorology -
  • Figure 2 - NOAA - Climate Prediction Center -
  • Figure 3 - International Research Institute for Climate and Society -
  • Figure 4 - NOAA - Climate Prediction Center -

Southwest Climate Outlook Monsoon Tracker - October 2018

Friday, October 19, 2018

The precipitation rankings for the months that encompass the monsoon period (see Fig. 3 on p. 2) smooth out the variability over space and time that is characteristic of this season. The cumulative totals for the monsoon for most of the major metropolitan areas in the region (Fig. 1) came in at or above average, with the exception of El Paso.

Monthly rankings show that June—which is typically dry, often with little actual precipitation at all in the Southwest—was wetter than normal across much of the borderlands region of Arizona and New Mexico (Fig. 2). This was almost entirely due to Tropical Storm Bud, which brought rain to the area in mid-June. Widespread precipitation occurred across the Southwest in July, and while a few areas only received below-normal precipitation, most of the region was at or above normal for the month (Fig. 3). August flipped that script, and while there were wide swaths of Arizona and New Mexico that received average to above-average rainfall, south-central New Mexico, parts of southern Arizona, and the Four Corners region in particular, lagged behind (Fig. 4). In September, southeastern Arizona and the lower two-thirds of New Mexico received average to above-average precipitation, but this was largely due to the incursion of tropical moisture in the latter half of the month. Outside that area, the region was generally devoid of widespread precipitation, with the Four Corners region continuing to be the epicenter of below-average to record-driest conditions (Fig. 5).

Monsoon totals (Figs. 6a-b on p. 5) demonstrate the range of precipitation across the two-state region. Percent of normal precipitation (Figs. 7a-b) and percent of days with rain (Figs. 8a-b) describe aspects of the monsoon that shape local perceptions of the monsoon’s performance (i.e. how much compared to normal, and whether rain fell in just a few intense days or over many less intense days).

Online Resources

  • Figure 1 - CLIMAS: Climate Assessment for the Southwest -

    • Figure 1 Data:
  • Figures 2-5 - Western Regional Climate Center -
  • Figures 6-8 - UA Climate Science Application Program -

Southwest Climate Outlook October 2018 - Climate Summary

Thursday, October 18, 2018

Precipitation and Temperature: Precipitation in September ranged from average to above average in New Mexico and from below average to much-above average in Arizona (Fig. 1a). September temperatures were warm throughout the region, ranging from much-above average to record warmest in Arizona and mostly above average to much-above average in New Mexico (Fig. 1b). Year-to-date precipitation was mostly average to below average in Arizona and New Mexico (Fig. 2a). Year-to-date temperatures were much-above average to record warmest across the region (Fig. 2b).

Monsoon Recap: The cumulative rainfall totals for June 15 – Sept. 30 blunt some of the monsoon variability seen across Arizona and New Mexico. Most of the region recorded normal to above-normal precipitation except for the Four Corners area, where rainfall ranged from below normal to record driest (Fig. 3). A closer look at statewide monthly totals and specific weather stations highlights the variability of the monsoon (see Monsoon Recap for details).

Drought: Water-year precipitation (Oct. 1 to present) was below normal to record driest for most of Arizona and ranged from above normal to record driest in New Mexico. More broadly, most of the Southwest experienced below normal or lower precipitation totals, with the driest conditions centered on the Four Corners region (Fig. 4). Recent iterations of the US Drought Monitor have identified drought category improvements in southern Arizona as a result of tropical storm activity in early October (Fig. 5). This highlights the ongoing challenge of monitoring drought in an arid region, as extreme precipitation events can certainly help some locations make up their cumulative precipitation deficits, but it is less clear how localized intense precipitation and flooding improves long-term drought conditions. Despite the short-term upticks in precipitation observed locally, most of the Southwest is still affected by longer-term, cool-season precipitation deficits that have accumulated over the past few decades under persistent annual drought conditions in the Southwest.

Tropical Storms: The eastern North Pacific hurricane season has been very active, with 20 named storms at the time of this writing (Fig. 6), including nine major hurricanes (category 4 or above). NOAA forecasted 14-20 named storms and seven major hurricanes, so we’re now at the high end of their prediction, and the season doesn’t end until Nov 30. This year is currently tied with 1992 for the most intense Pacific hurricane season on record, with an Accumulated Cyclonic Energy of 295, and could break the record if any additional storms develop or persist. In the Southwest, recent notable events include widespread precipitation from tropical depression Nineteen-E Sept. 19-20, the swath of extreme precipitation observed with Tropical Storm Rosa in early October, and more widespread precipitation activity linked to Tropical Storm Sergio in mid-October (see Tropical Storm Activity Tracker).

El Niño Tracker: Oceanic and atmospheric indicators are still within the range of ENSO-neutral conditions, but they are very likely moving towards an El Niño event in 2018. This shift is reflected in recent models and forecasts, which identify an approximately 75-percent chance of an El Niño event by the end of 2018. Most forecasts are calling for a weak event but a few suggest that a moderate event could develop (see El Nino tracker for details).

Precipitation and Temperature Forecast: The three-month outlook for November through January calls for increased chances of above-normal precipitation in Arizona and New Mexico (Fig. 7, top), and increased chances of above-average temperatures for the entire western United States (Fig. 7, bottom).

Online Resources

  • Figures 1-2 - National Centers for Environmental Information -
  • Figures 3-4 - Western Regional Climate Center -
  • Figure 5 - U.S. Drought Monitor -
  • Figure 6 - NWS National Hurricane Center -
  • Figure 7 - NOAA - Climate Prediction Center -