Climate Impacts and Outlook

Highlights for Hawaii and the U.S. Affiliated Pacific Islands

Weather Research & Forecasting Model (WRF) – model simulation (2-km resolution) of 10-meter wind speed (knots) and wind direction across Maui on 8/8/23 4:00 p.m. HST. The simulation shows strong downslope winds (35 knots = 40 mph) out of the northeast impacting West Maui. Source: Department of Atmospheric Sciences, UH, Manoa.

Landsat 8 satellite image of active fires (in yellow) on Maui, including Lahaina, at 10:25 p.m. on 8/8/23. The image is composed of shortwave infrared light observed by the Operational Land Imager on Landsat 8. Source: NASA Earth Observatory.

Post-fire aerial photograph of destruction at the Lahaina Harbor. Image credit: The Maui News.

Wildfires – On the evening of 8/8/23, an outbreak of wildfires impacted parts of Maui with catastrophic effects occurring in the historic town of Lahaina, West Maui. The wildfires quickly spread across Lahaina decimating the town with ~97 people perishing and over 2,200 structures either damaged or destroyed. It is estimated that nearly 86% of Lahaina was destroyed in the fires leaving several thousand residents displaced and in need of shelter. In addition, areas of the upper Kula region of Maui were also affected by the wildfires with 19 homes destroyed, according to the County of Maui. In terms of the antecedent climate conditions in Maui during the summer months (prior to the fires), below-normal rainfall was observed in West Maui and in Upcountry Maui causing the U.S. Drought Monitor to introduce areas of moderate to severe drought on the weekly map starting in mid-July with drought conditions intensifying during early August. Looking at observational station data for Lahaina and Kula preceding the wildfire outbreak, the Lahainaluna observing station (NWS COOP #51578) recorded 0.40 in. (25% of normal) of rainfall during Jun-Aug 2023 period, while the Kula Experiment Station site observed 0.37 in. (25% of normal), according to the NOAA Regional Climate Center’s SC-ACIS system and the National Weather Service (NWS) Forecast Office in Honolulu. In terms of the vegetation conditions, Normalized Difference Vegetation Index (NDVI) data (metric used to quantifying vegetation greenness, density, and plant health) from the NASA/USGS Landsat satellite for early August 2023 revealed areas of abnormally dry vegetation (as compared to long-term averages for the period) around West Maui and Upcountry Maui. Lastly, observed maximum wind gusts on the day of the wildfire outbreak (8/8/23) reached 62 mph at Maalaea Bay, according to the NWS. In response to the devastating fires, President Biden officially declared a major disaster on 8/10/23 ordering Federal aid to supplement state and local recovery efforts in the areas affected by the wildfires

Water Resources – In Majuro (RMI), reservoir storage reached 88% of total capacity (36,000,000 gallons) on 8/31/23. In Maui, Oahu, and Kauai, observed monthly average streamflows (August) on numerous rivers and streams were well-below normal (ranging from the 2nd-20th percentile), according to the U.S. Geological Survey.

Facilities and Infrastructure – In American Samoa, heavy rainfall (7/12-18) caused a landslide in the village of Amanave on the west side of the island of Tutuila on 7/18/23.

Seasonal sea surface temperature anomaly map for 6/4/23 to 9/2/23 (left) and 3-month seasonal precipitation anomalies for the June–August 2023 period (right). Areas with above-normal precipitation are depicted in green while areas with below-normal amounts are depicted in brown. Source: NOAA PSL, IRI, NOAA CPC CAMS-OPI.

By the end of the JJA period, SSTs were above-normal across the central and eastern tropical Pacific Ocean with an El Niño Advisory in effect (9/14/23). According to the latest NOAA CPC update (9/14/23), Niño region SST departures were above normal across the equatorial Pacific Ocean with Niño 3.4 at 1.6ºC, Niño 3 at 2.2ºC, Niño 1+2 at 2.9ºC, and Niño 4 at 1.1ºC.

During the JJA period, below-normal sea levels were observed across areas of the northwestern tropical Pacific Ocean with the highest sea level anomalies in USAPI occurring around Palau and western FSM (5-10 cm below normal) as well as in areas of the northeastern Pacific Ocean away from the coast. Elsewhere in the Pacific, above-normal sea levels were observed across the central and eastern equatorial Pacific (5-15 cm above normal) by August. Overall, the basin-wide sea level pattern was consistent with El Niño conditions and the exceptionally negative Pacific Meridional Mode, according to the University of Hawaii Sea Level Center.

During the JJA period, most of the USAPI was drought-free, with exception of short-term drought development observed in American Samoa in August. Median precipitation for the JJA period was above normal across much of the USAPI with exception of areas of RMI and American Samoa. For JJA, Airai (Palau) recorded 57.11 in. (109% of normal). In FSM, Yap observed 61.37 in. (139% of normal, 3rd wettest), Kapingamarangi 52.77 in. (138% of normal, wettest on record), Pohnpei 71.91 in. (155% of normal, wettest on record), Lukunor 35.77 in. (87% of normal), Kosrae 58.69 in. (128% of normal), and Chuuk 44.52 in. (115% of normal). In the Mariana Islands, Saipan observed 26.09 in. (106% of normal) and Guam 37.16 in. (109% of normal). In the RMI, Majuro observed 30.5 in. (89% of normal) for JJA, while Kwajalein logged 22.24 in. (82% of normal). In American Samoa, precipitation was below normal (13.71 in.,78% of normal, 6th driest August on record) at Pago Pago. Across much of the Hawaiian Islands, below-normal rainfall conditions prevailed during the JJA period, with moderate to severe drought conditions observed across areas of the island chain, according to the U.S. Drought Monitor. For the JJA period, Lihue observed 3.22 in. (55% of normal), Honolulu 0.7 in. (38% of normal), Molokai 0.8 in. (39% of normal), Kahului 0.67 in. (54% of normal), Kailua Kona 0.84 in. (47% of normal), and Hilo 14.7 in. (53% of normal).

During the MAM period, most of the USAPI were drought-free, with exception of short-term drought conditions observed in RMI in Wotje (Mar-Apr), Kwajalein (Mar-Apr), and in FSM in Kapingamarangi during March. Median precipitation for the MAM period was above normal across much of the USAPI. For MAM, Airai (Palau) recorded 38.87 in. (129% of normal). In FSM, Yap observed 22.4 in. (116% of normal), Kapingamarangi 35.43 in. (138% of normal), Pohnpei 69.82 in. (126% of normal, 6th wettest May on record), Lukunor 24.73 in. (70% of normal, 6th driest MAM on record), Kosrae 47.3 in. (87% of normal), and Chuuk 45.8 in. (133% of normal). In the Mariana Islands, Saipan observed 13.01 in. (215% of normal, 3rd wettest MAM on record) and Guam 41.61 in. (390% of normal, wettest MAM and May on record). In the RMI, Majuro observed 35.7 in. (139% of normal) for MAM, while Kwajalein logged 37.48 in. (217% of normal). In American Samoa, precipitation was above normal (41.78 in.,126% of normal) at Pago Pago. Across much of the Hawaiian Islands, above-normal rainfall was observed for the MAM period, with drought-free conditions observed across most of the island chain with exception of moderate drought observed in areas of Central/West Maui in April and in the North Kohala district on the Big Island during May, according to the U.S. Drought Monitor. For the MAM period, Lihue observed 14.81 in. (151% of normal), Honolulu 5.49 in. (139% of normal), Molokai 6.5 in. (114% of normal), Kahului 3.02 in. (65% of normal), Kailua Kona 3.42 in. (153% of normal), and Hilo 21.96 in. (74% of normal).

In the Northwest Pacific region (west of 135ºE), tropical cyclone (TC) activity has been above normal for the 2023 season, with 12 named storms with an Accumulated Cyclone Energy (ACE) Index of 211 (normal 143) by 9/5/23. In the Northeast Pacific region (east of 180ºW), the ACE Index has been above normal (105.6 by 9/5/23—normal for the date 86.9) with 10 named storms since late June including the powerful, long-lasting Hurricane Dora (~8/1-8/12 as a hurricane/typhoon) which developed in the Eastern Pacific during early August of the coast of El Salvador. Dora tracked westward across the Pacific Ocean intensifying to a Category 4 hurricane with sustained winds of 145 mph on 8/5/23. The hurricane eventually crossed the International Date Line (8/11) and was reclassified as Typhoon Dora.

According to the latest ENSO prediction model simulations (above right), there is relatively strong agreement amongst the dynamical models in the IRI ENSO prediction plume of gradual strengthening of positive SST anomalies during the Sept-Nov 2023 period and continuation into the Northern Hemisphere winter (>95% chance through January-March 2024) in association with the on-going El Niño event. Moreover, the probability of a “strong” El Niño to develop (Nov 2023-Jan 2024) has increased to 71%, according to NOAA CPC.

NOAA’s Coral Reef Watch four-month coral bleaching heat stress outlook (Sept 2023-Dec 2023) calls for a high probability (90%) of high heat stress (Alert Level 1-2) developing in areas of the tropical Pacific Ocean extending from ~125º W to ~160º E. Moreover, a heat stress Watch is forecast for areas of RMI, eastern FSM, Guam, CNMI and portions of the Hawaiian Islands.

During the period of September 2023 through November 2023, above-normal precipitation is forecasted for areas of USAPI, including most of FSM (Chuuk, Kosrae, Pohnpei) and RMI (Kwajalein, Majuro). Average to above-average rainfall is forecasted for the Yap, Guam, CNMI (Saipan) and average rainfall for Palau. Conversely, average-to-below normal precipitation is expected for American Samoa, while below-normal precipitation is expected in the Hawaiian Islands, according to the NOAA Pacific ENSO Applications Climate Center.