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In last week’s post, I mentioned there were 10 strong El Niño events since 1970 based on the Climate Prediction Center’s (CPC) Relative Oceanic Niño Index (RONI). I also showed the tropical cyclone (TC) tracks for the 5 central North Pacific (CNP) seasons with El Niño events reaching strong intensity during the main tropical cyclone activity months of July through September. These seasons occurred in 1972, 1982, 1987, 1997, and 2015.
With all the hype about how strong this year’s El Niño will/could be, I thought it would be interesting to show what the TC season tracks were like during El Niño events that became strong in the summer. That was the motivation behind last week’s post. The evolution of these events, as tracked by the RONI, are shown as the red lines in the graph below. However, based on this year’s RONI plot (green line), it looks like examining the “other 5” years would be useful since it seems to line up better with the cluster of black lines. So that’s what I’m going to cover in this week’s post.
Plot of the RONI vs. 3-month seasons from December-January-February (DJF) through November-December-January (NDJ) during years with strong El Niño events. The five red lines show the El Niños that became strong during the peak TC activity months. The black lines show the “other five”, which are the El Niños that became strong later in the year. The single green line shows the RONI through the end of May 2026. Data for the plots are from the CPC’s RONI page.
The seasons for the “other five” occurred in 1986, 1991, 2002, 2009, and 2023. These El Niño events reached “strong” or even “very strong” (a.k.a. “Super El Niño”) levels, but just later in the year after the usual peak of CNP TC activity. Similar to last week, I took data from the International Best Track Archive for Climate Stewardship (IBTrACS) database, and plotted the tracks for these five “late bloomer” years.
In 1986, this event did not reach El Niño status until the second half of the summer, but strengthened quickly in the fall to become a strong event by the end of the year. There were seven tropical cyclones during the season. Only one developed in the CNP, with the rest coming in from the eastern North Pacific (ENP). Most were weak and remained far from the main Hawaiian Islands. The exception was Hurricane Estelle, which passed south of the Big Island as a Category 1 hurricane on the Saffir-Simpson Hurricane Wind Scale. It was close enough to the island chain to produce heavy rain and gusty winds, especially on the Big Island, but the main story was the large, damaging surf. The Kapoho Vacationland subdivision on the east side of the Big Island had significant damage, including five homes destroyed (Au et al. 1987). I remember this event not because I was on the Big Island at the time, but because Harry Kim, the former Hawaiʻi County Civil Defense Administrator and later multi-term mayor always talked about how his home in Vacationland suffered significant surf damage.
Track graphic of CNP tropical cyclones in 1986. Portions of the tracks east of 140W longitude and west of the International Dateline are not included. Plot points are in Coordinated Universal Time (UTC), which is 10 hours ahead of Hawaiian Standard Time (HST). Thus, 0000 UTC is 2 PM HST of the previous day, and 1200 UTC is 2 AM HST of the same day. Data for the graphic are from the International Best Track Archive for Climate Stewardship (IBTrACS) database hosted by the NOAA National Centers for Environmental Information (NCEI).
Sometimes El Niño events get a head start from events that fail to fully develop the previous year. One of these occurred in 1991. However, after reaching El Niño status in the spring, it remained at weak levels until the fall when it rapidly intensified to a very strong event at the end of the year. Only three TCs moved into the CNP during the season, which is actually a below normal total, and all of them moved in from the ENP basin. Fefa threatened the Big Island as it moved generally west, but dissipated just before the center made landfall. It was close enough to produce gusty winds, high surf, and localized flash flooding, mainly on the Big Island (Chun et al. 1992).
Same as the above map, but for the 1991 season.
The El Niño in 2002 developed in the spring and steadily strengthened through the summer and fall. It peaked just at the strong threshold of +1.5C late in the fall. The CNP had a bit of an atypical season because there were more TCs named west of 140W longitude than to the east. As a result, three out of the five TCs had Hawaiian names. All remained far from the state.
Same as the above map, but for the 2002 season.
In 2009, the El Niño event didn’t start until late summer or early fall, but it rapidly intensified and peaked just above the strong threshold at the end of the year. It was a fairly active TC season with seven systems, six of which occurred in August, making for a busy month at the Central Pacific Hurricane Center. Felicia posed the greatest threat to the main Hawaiian Islands but it dissipated east of Maui before making landfall. It did produce high surf along the east-facing shores, and remnant moisture fueled flash flooding over portions of the state (Kimberlain et al. 2010). Neki developed later in the season far south of the Hawaiian Islands, but moved northwest, then northeast, and passed through the Papahānaumokuākea Marine National Monument. There were no reports of significant damage during its passage but it did force the evacuation of staff from French Frigate Shoals.
Same as the above map, but for the 2009 season.
Finally, the 2023 event was similar to 2002 in that it became an El Niño in the spring and also peaked at the strong threshold at the end of the year. Four TCs occurred in the CNP this year, and all moved in from the ENP as general west-movers. I worked as one of the hurricane forecasters as Calvin passed just south of the Big Island, causing windy conditions and some flash flooding. The 2023 season is also known for Hurricane Dora, which traversed the entire CNP basin as a hurricane. The tropical cyclone report on Dora from the National Hurricane Center stated that “the hurricane played an indirect meteorological role in the devastating wildfires on Maui, Hawaiʻi” (Bucci et al. 2026). There are other studies that disagree with this assessment (e.g. Mass and Ovens 2024).
Same as the above map, but for the 2023 season.
The TC season numbers in the CNP for the “other five” do not show as wide a range as the seasons where El Niño became strong during the summer. Interestingly, only two of these seasons, 1986 and 2009, had above normal TC totals. The rest were near or below normal. None of the TCs in the five seasons shown here directly hit the main Hawaiian Islands. However, several were close enough to cause impacts from enhanced winds, heavy rainfall, and/or high surf. This is why the National Weather Service always implores people to not focus solely on the center of the tropical cyclone as impacts can occur far from this point.
References
Au, W., A. Chun, H. Rosendal, and R. Sewake, 1987: 1986 Tropical Cyclones – Central North Pacific. NOAA Tech. Memo. NWSTM PR-32, 36 pp.
Bucci, L., A. Gibbs, and J. Jelsema, 2026: Tropical Cyclone Report – Hurricane Dora.
Chun, A. K. T., R. T. Martin, H. E. Rosendal, and G. H. Trapp, 1992: 1991 Tropical Cyclones – Central North Pacific. NOAA Tech. Memo. NWSTM PR-37, 21 pp.
Kimberlain, T. B., D. Wroe, and R. D. Knabb, 2010: Tropical Cyclone Report – Hurricane Felicia.
Mass, C. and D. Ovens, 2024: The Meteorology of the August 2023 Maui Wildfire. Wea. Forecasting, 39, 1097-1115.
Wroe, D., 2010: Tropical Cyclone Report – Hurricane Neki.