How remnants of Hurricane Polo contributed to St. Joseph’s wettest September in 10 years

For the second time in just over two weeks, repeated rounds of steady rain have added up across the Mid-Missouri River Valley. Like recent rainfall events, some area waterways climbed to minor or moderate flood stage, although widespread major flooding wasn't an issue. This bout of wet weather brought the September rainfall total to 7.23 inches at Rosecrans Memorial Airport, the wettest September in St. Joseph since 2016 when over 8 inches of rain was recorded. 

The unique nature of this week’s local soaker is its origin, partially attributed to plumes of Pacific moisture associated with the remnants of Hurricane Polo. Once a monster Category 5 storm, Polo made landfall at Baja California on Mexico’s Pacific Coast as a Category 2 late Monday night, Sep. 28 2026.

Polo rapidly weakened following landfall, and its remnants tracked northeast contributing to flash flooding and severe weather in the southwestern United States from Arizona to Texas. Over the following days, waves of rain and storms swirled northeastward into the Central Plains as the disturbance linked up with a cold front slowly pushing through the region. 

The 'leftovers' of tropical systems occasionally bring clouds and rain to Northwest Missouri and Northeast Kansas every few years, most often originating from the Atlantic side. Moisture and remnant circulations from Pacific tropical systems making it to the Central Plains and Midwest is more rare. 

It’s been a decade since something similar happened with regards to a Pacific tropical system indirectly delivering moisture this far inland. Hurricane Newton made landfall in a similar location as a Category 1 storm, its remnants eventually helping produce copious amounts of rainfall across the Mid-Missouri River Valley. Interestingly, this was in September of 2016, the last time St. Joseph received monthly rainfall comparable to September 2026.

The 2026 hurricane season has been anomalous between the Pacific and Atlantic basins. As of October 1st not a single hurricane has formed in the Atlantic Ocean. That hasn’t happened in over a century. Meanwhile, the Pacific has been a hot-bed of organized tropical activity with 18 hurricanes so far this season. 

In large part, this year’s record El Nino has been driving the lopsided hurricane season. El Nino is characterized by above average sea surface temperatures in the Tropical Pacific. While El Nino events take place every few years, the current El Nino is warmer than any in recorded history. A strong El Nino pattern is known to suppress tropical activity in the Atlantic due to an influx of wind shear aloft, while enhancing it in the tropical Pacific as warmer waters help fuel hurricane development.

Luckily, the next few days will be anything but tropical here in the heartland, with cool fall air and dry skies just in time for the weekend.