Traveling tropical disturbance increases rainfall across the Hawaiian Islands

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A new study by researchers at the University of Hawai'i at Mānoa revealed that the Madden–Julian Oscillation (MJO), a large-scale tropical disturbance that travels eastward through the tropics every 30–60 days, significantly influences climate conditions in Hawai'i. Their research, published recently in the Journal of Hydrometeorology, showed that during active MJO phases, rainfall increases across the islands, especially on windward slopes. In contrast, suppressed MJO phases tend to produce drier conditions.

"Understanding how the MJO affects Hawai'i'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 the UH Mānoa 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 Hawai'i 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 Hawai'i and the surrounding Pacific Ocean, including data from the Hawai'i 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," shared 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.

Sustainable water resources

Hawai'i is one of the most remote populated regions in the world, and communities across the islands rely heavily on local rainfall for water resources. This research advances scientific knowledge of the processes that influence Hawai'i's climate and can help improve forecasts one to three months in advance.

"Improving our understanding of rainfall variability is critical for water management, agriculture, and hazard preparedness," said Nash. "This work reflects the University of Hawai'i's mission to study the unique environmental systems that shape life in the islands and to provide science that benefits local communities."

More information

Audrey A. Nash et al, The Impact of the MJO on Climate in Hawai'i, Journal of Hydrometeorology (2026). DOI: 10.1175/jhm-d-25-0054.1

Key concepts

climatologydroughts

Provided by University of Hawaii at Manoa