2025 Monsoon Season Review

Review of the 2025 Monsoon Across the Southwest U.S.

1. Overview

For the third consecutive year, a significant portion of the Desert Southwest experienced below normal rainfall during the 2025 North American Monsoon (June 15 - Sept 30). Below normal rainfall was particularly evident in the Great Basin and Four Corners area, extending through northern and eastern Arizona, and the western third of New Mexico. Conversely, central and eastern New Mexico, as well as southern California through south-central Arizona, including the metropolitan areas of Phoenix and Yuma, recorded above-normal rainfall (Figs. 1-2). The above normal rainfall observed across these areas can be tied to a couple of intense rainfall events that occurred mostly during the month of September. Consistent with the long term trend, temperatures were well-above normal across much of the region (Fig. 3).

Fig. 1. Precipitation ranking for June - September 2025. Source: WestWide Drought Tracker.

Fig. 2. Percent of average precipitation between June 15th and September 30th, 2025. Source: CLIMAS/OSU PRISM.

Fig. 3. Temperature ranking for June - September 2025. Source: WestWide Drought Tracker.

Lightning data is one way of assessing how active a particular monsoon was. Not surprisingly, given the mostly negative rainfall anomalies, lightning activity for 2025 was below average across Arizona.  Data from the Vaisala National Lightning Detection Network (NLDN) shows the 2025 Monsoon having the third fewest total lightning strikes across Arizona since 1990 with just over 200,000 total strikes (Fig. 4). Approximately two-thirds of the total lightning activity across Arizona occurred from the middle of August through the end of September, coinciding with the most active portion of the 2025 Monsoon Season (Fig. 5).

Fig. 4. Total lightning strikes across Arizona for the monsoon season for each year between 1990 - 2025. Source: NLDN.

Fig. 5. Cumulative day-to-day total lightning strikes across Arizona for the monsoon season for each year between 1990-2025. Source: NLDN

In contrast to the 2022-2023 and 2023-2024 winter seasons, which experienced above normal precipitation, the 2024-2025 Winter Season registered well-below normal precipitation across much of the region. Combined with a very dry 2024 fall, drought substantially worsened across much of the southwestern U.S. with many areas falling under severe to extreme drought conditions (i.e. D2 or greater). Areas that registered below-normal monsoon rainfall observed unchanged drought conditions or worsened, whereas, areas that registered above-normal rainfall observed a slight improvement. (Fig. 6). 

Fig. 6. Depiction of drought conditions via the U.S. Drought Monitor prior to and after the monsoon.

2. Typical Monsoon Pattern

During the monsoon, the subtropical high pressure (often known as the “Monsoon High”) strengthens, expands, and drifts northward (Fig. 7). As it drifts northward during the course of the summer months, it causes a reversal in the overall wind pattern from west-to-east to east-to-west. This reversal in the wind pattern results in a significant increase in atmospheric moisture across the southwestern U.S and thus an increase in showers and thunderstorms.

Fig. 7. Animation showing the typical development, northward migration, and ultimate demise of the “monsoon high” through the summer. The black contours and red/blue colorfill represent the average height (in meters) of the 500 mb pressure level, representing the vertical middle of the atmosphere. The blue/magenta/cyan lines represent precipitable water (PWAT, the depth of water if water vapor in a vertical column of the atmosphere above a specific location is condensed into liquid) values of 1.0/1.5/2.0”. The inset trace is for Phoenix, AZ, showing the seasonal PWAT trend. Graphic produced by Paul Iñiguez, former Science and Operations Officer at NWS Phoenix. Data source: NCEP NARR.

The Monsoon season offers a temporary respite from the intense heat prevalent across much of the Desert Southwest during the summer months. The influx of moisture increases cloud cover, leading to periodic showers and thunderstorms. This helps limit surface heating and spread rain-cooled air to the ground, resulting in a temporary reduction in surface temperatures. For most of the Desert Southwest, approximately 50% of the annual precipitation occurs during the June through September period. Overall, the percentage of annual rainfall varies significantly from less than 20% across extreme western Arizona to almost 70% in the mountains of southern New Mexico and far west Texas (Fig. 8).

Fig. 8. The percent of annual rainfall during the monsoon months of June through September. Graphic produced by Paul Iñiguez, former Science and Operations Officer at NWS Phoenix. Data source: NCEI NClimGrid.

3. The 2025 Monsoon Pattern

The first part of the monsoon season, June 15 through August 15, was notably inactive with well-below normal rainfall. This inactivity was primarily due to a persistent area of low pressure in the western U.S., which displaced the subtropical high pressure to the south and east of the region (Fig. 9). Consequently, upper-level west and southwest flow prevailed, which consistently introduced dry air and severely limited thunderstorm development (Fig. 10).

Fig. 9. 500 mb Geopotential Height Composite Mean for the period of June 15th to August 15th, 2025. Source: NCEP/NCAR.

Fig. 10. Precipitable Water Composite Anomaly for the period of June 15th to August 15th, 2025. Source: NCEP/NCAR.

The weather pattern underwent a significant change during the latter half of August through September. An upper-level low pressure system was frequently situated off the southern California coast with the subtropical high pressure to the east (Fig. 11). This caused increased southerly flow, yielding enhanced moisture surges, including from the remnants of tropical systems that developed off the southwestern coast of Mexico (Fig. 12). Consequently, the environment became more conducive to more frequent thunderstorm activity, leading to above-normal rainfall, particularly in the month of September (Fig. 13).

Fig.11. 500 mb Geopotential Height Composite Mean for the period of August 15th to September 30th, 2025. Source: NCEP/NCAR.

Fig. 12. Precipitable Water Composite Anomaly for the period of August 15th to September 30th, 2025. Source: NCEP/NCAR.

Fig. 13. Precipitation ranking for September 2025. Source: WestWide Drought Tracker.

Significant Events During Monsoon 2025:

Some notable high impact events occurred during this monsoon within the NWS Phoenix county warning area (CWA), from significant flash flooding, to microburst wind damage, to large hail, and expansive dust storms:

August 25, 2025 - Dust storm and flash flooding 

• Widespread thunderstorm activity impacted much of southern California and southwest Arizona, with an additional complex of storms affecting southern and central Arizona. Significant flash flooding and heavy rainfall were observed across portions of southeast California through southwest Arizona. Simultaneously, across southern and central Arizona, a massive dust storm traveled from the Tucson area, up through Phoenix, and into southern Yavapai County, with numerous areas experiencing near-zero visibility.  A full event writeup can be accessed here: August 25: Massive Dust Storm and Flash Flooding

September 25-27 - Heavy rainfall, flash flooding, and severe storms

• A very slow moving low pressure system moving through the Desert Southwest resulted in a multi-day severe weather and flash flooding event. The most significant impacts were felt across south-central Arizona, where significant flash flooding was observed, including catastrophic flash flooding across the Globe/Miami area in southern Gila County. Even though flash flooding was the main impact, instances of microburst wind damage and large hail were also observed. A full event writeup can be accessed here: September 25-27: Heavy Rainfall/Flash Flooding & Severe Storms

4. NWS Weather Warnings During the 2025 Monsoon

Slightly more Flash Flood Warnings (FFW) were issued by NWS forecast offices across the southwestern U.S. during the 2025 Monsoon Season compared to the 2024 Monsoon Season, however, 2025 totals were still below the totals from the very active 2021 and 2022 seasons (Fig. 14). The areas with the highest counts of FFWs included Mohave County, AZ, most of central and eastern New Mexico, and west Texas, with a particular focus on burn scar areas. Though less frequent, other FFW hot spots included portions of southern California and central/southern Arizona, including cities such as Imperial, Yuma, Phoenix, Globe, and Tucson (Fig. 15). Conversely, most of northern and eastern Arizona and western New Mexico, saw very little in the way of FFWs. This spatial pattern matches the areas that recorded the greatest negative rainfall anomalies for the season. 

Fig. 14. Number of Flash Flood Warnings (FFW) issued by NWS Southwest Offices each year between June 15 - September 30 since 2008. Source: Iowa Environmental

Fig. 15. Monsoon 2025 Flash Flood Warning (FFW) Spatial Frequency.

Over 700 total Severe Thunderstorm Warnings (SVR) were issued by NWS forecast offices in the southwestern U.S. during the 2025 Monsoon Season, which ranks as the fourth highest count since the implementation of polygon-based warnings in October 2007 (Fig. 16). Consistent with past years, SVRs were most frequent in the lower elevations bordering the major mountain ranges. This includes major metropolitan areas like Phoenix, Tucson, and Las Vegas, where the risk of significant impacts is elevated, as well as across the High Plains of New Mexico and Texas. (Fig. 17).

Fig. 16. Number of Severe Thunderstorm Warnings (SVR) issued by NWS Southwest offices each year between June 15 - September 30 since 2008. Source: Iowa Environmental Mesonet

Fig. 17. Monsoon 2025 Severe Thunderstorm Warning (SVR) Spatial Frequency.

Despite observing well-above normal temperatures across much of the region throughout the summer months, the prominence of hazardous extreme heat in the lower elevations during 2025 was notably reduced compared to 2023 and 2024. Approximately 30 or fewer Extreme Heat Warning (EHW) days were recorded in Arizona in 2025, a notable drop from the over 40 days issued in each of the two previous years (Fig. 18-19). This decrease in EHW days can be attributed to the common 2025 summer weather pattern: a persistent area of low pressure positioned off the western United States, which limited the usual expansion of the subtropical high pressure into the Desert Southwest, thereby reducing the frequency of extreme heat episodes. The combination of the fewer extreme heat episodes and ongoing heat mitigation efforts likely contributed to a significant reduction in heat-related deaths in 2025. As reported by the Maricopa County Department of Public Health, through the end of October, the total confirmed number of heat-related fatalities was 333 in 2025 vs. 470 confirmed during the same period in 2024.

 Fig. 18. Total number of Extreme Heat Warning (EHW) Days per NWS Forecast Zone in Arizona for 2025. Source: Iowa Environmental Mesonet (Click on image for better resolution)

Fig. 19. Total number of Extreme Heat Warning (EHW) Days per NWS Forecast Zone in Arizona for 2023 (left) and 2024 (right). Source: Iowa Environmental Mesonet (Click on images for better resolution)