The University of Hawaiʻi at Mānoa has identified a large-scale tropical disturbance called the Madden-Julian Oscillation (MJO) as a significant driver of the islands' climate, including extreme events, such as the extraordinary rainfall Hawaiʻi experienced in March and April. This weather pattern travels eastward through the tropics every 30–60 days and, according to the study , significantly boosts rainfall during its active phases, particularly on windward slopes.
This research advances scientific knowledge of the processes that influence Hawaiʻi's climate and can help improve forecasts one to three months in advance.
"Understanding how the MJO affects Hawaiʻi's climate helps explain rainfall variability on timescales of weeks to months," said Audrey Nash, lead author of the study and doctoral candidate in the Department of Atmospheric Sciences in UH Mānoa's School of Ocean and Earth Science and Technology . "The MJO evolves slowly and can be monitored in real time. Understanding its influence can help scientists and forecasters better anticipate periods of heavy rainfall, drought conditions, and shifts in weather patterns across the islands."
High-resolution data reveals the pattern
While the MJO was known to influence weather patterns across the tropics, its impact on Hawaiʻi had not previously been examined in detail at timescales of one to three months.
Nash and Giuseppe Torri, associate professor of atmospheric sciences, analyzed long-term, high-resolution atmospheric and rainfall datasets covering Hawaiʻi and the surrounding Pacific Ocean, including data from the Hawaiʻi Climate Data Portal . By compositing rainfall, temperature and atmospheric variables across different phases of the MJO, they identified consistent patterns showing how the MJO modulates rainfall and climate conditions across the Hawaiian Islands.
"We expected a small impact, but it was surprising how consistently rainfall across the islands responds to active and suppressed phases of the MJO," said Nash.
Active phases of the MJO are also associated with cooler temperatures, higher humidity and stronger northeasterly winds across the islands. The authors note that these patterns appear to be linked to large-scale atmospheric responses to the MJO, including slow moving Rossby waves in the central North Pacific and strengthening of the local Hadley Circulation, a major feature of global atmospheric movement that cools the tropics and warms the poles.
"Improving our understanding of rainfall variability is critical for water management, agriculture, and hazard preparedness," said Nash. "This work reflects the University of Hawaiʻi's mission to study the unique environmental systems that shape life in the islands and to provide science that benefits local communities."
The post Traveling tropical disturbance increases Hawaiʻi rainfall in cycles first appeared on University of Hawaiʻi System News .
