Prognostic Meteorological Discussion
Issued by NWS
Issued by NWS
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FXHW40 KWBC 211231
PMDHCO
Prognostic Discussion for Long-Lead Hawaiian Outlooks
NWS Climate Prediction Center College Park MD
830AM EDT Thu Aug 21 2025
MONTHLY FORECAST DISCUSSION VALID SEPTEMBER 2025
Sea-surface temperature (SST) anomalies in the range of 0 to +1 degrees Celsius
(C) were observed around the Hawaiian Islands (Kauai, Oahu, Maui and the Big
Island) during the previous week.
From January through July 2025, rainfall total accumulations were:
Lihue Airport 10.85 inches (55 percent of average)
Honolulu Airport 8.97 inches (103 percent of average)
Kahului Airport 6.61 inches (68 percent of average)
Hilo Airport 33.89 inches (53 percent of average)
Most climate models of the North American Multi-Model Ensemble (NMME) and the
International Multi-Model Ensemble (IMME/C3S) predict positive SST anomalies
around most of the Hawaiian Islands in September 2025. Most models predict weak
or near zero SST anomalies near the southeastern Hawaiian Islands in September
2025. Based on model SST and surface air temperature forecasts, above normal
temperatures are favored for Kauai (Lihue), Oahu (Honolulu) and Maui (Kahului)
with greater probabilities for the northwestern islands of Oahu and Kauai.
Equal chances (EC) for above, near or below normal temperatures are indicated
for the Big Island of Hawaii (Hilo) in September 2025, where tools are less
consistent.
For the September 2025 precipitation outlook, the probability of below normal
precipitation is elevated for all islands of Hawaii, with greater probabilities
for the southeastern islands compared to the northwestern islands. The outlook
is consistent with most models of the NMME and IMME.
TEMPERATURE PRECIPITATION
FCST AVE LIM FCST BLW MEDIAN ABV
Hilo EC 76.4 0.5 B55 8.0 9.3 11.0
Kahului A45 79.3 0.4 B50 0.1 0.2 0.5
Honolulu A55 81.8 0.4 B45 0.4 0.6 0.8
Lihue A60 79.4 0.3 B40 1.7 1.9 2.6
SEASONAL FORECAST DISCUSSION VALID SON 2025 - SON 2026
Refer to the prognostic discussion of the long-lead seasonal outlooks for the
contiguous U.S. (CONUS) and Alaska for further description of the El Nio
Southern Oscillation (ENSO) outlook and other climate conditions relevant to
the seasonal outlook.
ENSO-neutral conditions continued into August. Equatorial sea surface
temperatures (SSTs) are near-to-below average across much of the central
tropical Pacific Ocean. SST anomalies were slightly negative in recent weeks
over the east-central equatorial Pacific, with Nio 3.4 anomalies ranging
between 0.0 and -0.5 C since mid-July. Positive SST anomalies are observed over
the western and far eastern equatorial Pacific Ocean. Above-average subsurface
ocean temperatures persist across most of the western equatorial Pacific Ocean
to depths as great as 200 meters, while below-average subsurface ocean
temperatures expanded since July across much of the eastern equatorial Pacific.
Above-average outgoing longwave radiation (OLR), associated with suppressed
convection and precipitation, are observed in the western equatorial Pacific
Ocean. Low-level (850-hPa) wind anomalies are easterly over the east-central
and eastern equatorial Pacific, while upper-level (200-hPa) wind anomalies are
westerly over the eastern equatorial Pacific.
Most dynamical and statistical models predict a continuation of ENSO-neutral
conditions through the end of boreal summer into the beginning of autumn. Some
models, such as the NCEP Climate Forecast System (CFSv2), the CPC SST Canonical
Correlation Analysis (CCA), and CPC Markov models, predict the likely
development of a La Nia in autumn through forecasts of SST anomalies below
the -0.5 C threshold averaged for the Nio 3.4 region. The CPC ENSO Outlook
forecasts ENSO-neutral conditions with a 56% chance in the three-month
August-September-October season. However, La Nia conditions are more likely
than ENSO-neutral in autumn and early winter 2025-26. The probabilities of
ENSO-neutral and La Nia conditions are nearly equal in the
December-January-February winter season with increasing chances of ENSO-neutral
conditions thereafter. The increasing likelihood of La Nia conditions alters
precipitation probabilities in the Hawaii Seasonal Outlook, increasing the
probability of above normal precipitation in boreal winter. However the state
of ENSO at longer lead times is uncertain, such that precipitation forecasts
are somewhat uncertain after about five months lead time.
Enhanced probabilities for above normal temperatures are predicted in the
outlook for Lihue, Honolulu, and Kahului beginning in
September-October-November (SON) and for Hilo in October-November-December
(OND) 2025, through January-February-March (JFM) 2026, supported by nearly all
dynamical model forecasts from the NMME and C3S. Probabilities for above normal
temperatures are greater for northwestern islands of Hawaii in early seasons,
exceeding 65 percent for Linue, following calibrated model guidance from the
NMME. Due to increasing uncertainty in the state of ENSO and weakening signals
in forecast guidance at longer leads, equal chances (EC) for above, near or
below normal temperatures are indicated for Hawaii beginning in JFM 2025-26 and
extending through longer leads.
Enhanced probabilities for below normal precipitation are forecast over the
southeastern islands, Maui and the Big Island for SON 2025, consistent with
most dynamical model forecasts. Enhanced probabilities for above normal
precipitation are forecast for the islands of Oahu and Kauai beginning in OND
2025 and for Maui and the Big Island beginning in November-December-January
(NDJ), continuing through JFM 2026, consistent with most dynamical model
forecasts, as well decadal timescale precipitation trends. Equal chances (EC)
for above, near or below normal precipitation are indicated for some early
seasons with uncertainty in the transition from drier conditions in boreal
summer and autumn to wetter conditions in boreal winter. Beginning in
February-March-April (FMA) 2026 and extending through longer leads, EC is
indicated in the seasonal precipitation outlook, due to uncertainty in the
state of ENSO and weaker signals in forecast tools.
Hilo
TEMPERATURE PRECIPITATION
FCST AVE LIM FCST BLW MEDIAN ABV
SON 2025 EC 76.2 0.4 B45 24.3 30.2 40.8
OND 2025 A40 75.5 0.4 EC 28.3 34.5 42.0
NDJ 2025 A40 74.2 0.4 A40 26.4 36.6 43.0
DJF 2026 A40 72.8 0.4 A45 19.6 30.2 33.3
JFM 2026 A40 71.8 0.4 A45 22.0 32.0 44.5
FMA 2026 EC 71.7 0.4 EC 24.6 34.1 45.5
MAM 2026 EC 72.0 0.5 EC 22.5 28.4 34.0
AMJ 2026 EC 72.9 0.5 EC 21.4 23.7 29.0
MJJ 2026 EC 74.0 0.4 EC 20.2 27.5 29.1
JJA 2026 EC 75.2 0.4 EC 19.4 27.2 31.4
JAS 2026 EC 76.1 0.4 EC 25.2 28.6 33.4
ASO 2026 EC 76.4 0.4 EC 26.1 28.8 33.3
SON 2026 EC 76.2 0.4 EC 24.3 30.2 40.8
Kahului
TEMPERATURE PRECIPITATION
FCST AVE LIM FCST BLW MEDIAN ABV
SON 2025 A50 79.1 0.4 B40 2.1 3.3 4.8
OND 2025 A45 77.8 0.4 EC 4.2 5.3 8.1
NDJ 2025 A45 75.9 0.4 A40 5.2 7.6 9.5
DJF 2026 A40 73.8 0.4 A45 4.6 6.9 8.7
JFM 2026 A40 72.5 0.4 A45 4.2 6.2 8.2
FMA 2026 EC 72.3 0.4 EC 3.2 4.1 6.4
MAM 2026 EC 73.0 0.4 EC 2.5 3.5 4.6
AMJ 2026 EC 74.3 0.5 EC 1.2 1.6 2.2
MJJ 2026 EC 76.0 0.5 EC 0.7 1.1 1.8
JJA 2026 EC 77.7 0.4 EC 0.7 1.1 1.5
JAS 2026 EC 79.0 0.4 EC 0.8 1.1 1.6
ASO 2026 EC 79.4 0.4 EC 0.8 1.6 2.5
SON 2026 EC 79.1 0.4 EC 2.1 3.3 4.8
Honolulu
TEMPERATURE PRECIPITATION
FCST AVE LIM FCST BLW MEDIAN ABV
SON 2025 A60 81.4 0.4 EC 2.5 4.0 5.6
OND 2025 A55 80.0 0.4 A40 4.4 6.4 8.5
NDJ 2025 A45 77.7 0.5 A45 3.9 5.6 8.8
DJF 2026 A40 75.3 0.5 A50 3.7 5.6 8.6
JFM 2026 A40 73.9 0.4 A50 2.1 4.6 7.8
FMA 2026 EC 73.8 0.4 EC 1.9 3.2 4.7
MAM 2026 EC 74.8 0.4 EC 1.8 2.6 3.0
AMJ 2026 EC 76.3 0.4 EC 1.2 1.6 1.8
MJJ 2026 EC 78.2 0.4 EC 0.8 1.4 1.6
JJA 2026 EC 79.9 0.4 EC 0.7 0.8 1.3
JAS 2026 EC 81.3 0.4 EC 1.0 1.4 1.7
ASO 2026 EC 81.7 0.4 EC 1.6 2.4 3.1
SON 2026 EC 81.4 0.4 EC 2.5 4.0 5.6
Lihue
TEMPERATURE PRECIPITATION
FCST AVE LIM FCST BLW MEDIAN ABV
SON 2025 A65 79.1 0.3 EC 9.2 10.0 11.2
OND 2025 A55 77.8 0.3 A40 9.2 11.7 15.6
NDJ 2025 A45 75.7 0.3 A45 8.6 12.1 16.9
DJF 2026 A40 73.6 0.4 A50 7.5 8.4 14.0
JFM 2026 A40 72.2 0.4 A50 6.5 8.8 13.8
FMA 2026 EC 72.1 0.5 EC 5.8 8.4 9.9
MAM 2026 EC 72.8 0.5 EC 5.3 6.6 8.0
AMJ 2026 EC 74.2 0.5 EC 4.7 5.5 6.0
MJJ 2026 EC 76.0 0.5 EC 4.9 5.4 5.9
JJA 2026 EC 77.7 0.4 EC 4.4 5.3 6.9
JAS 2026 EC 79.0 0.3 EC 5.3 6.1 7.8
ASO 2026 EC 79.4 0.3 EC 6.2 7.9 8.4
SON 2026 EC 79.1 0.3 EC 9.2 10.0 11.2
FORECASTER: Dan Collins
Anomalies are based on the 1991-2020 means.
CLARIFICATION: EC indicated equal chances that the predicted parameter will
fall into any one of the three categories, whose boundaries are specific in the
tables above. A forecast specification of EC means there is no particulate tilt
of the odds toward above normal or below normal conditions in the outlook. For
example A40 means a 40% chance that the average temperature or total
precipitation will be in the above normal class, B40 means a 40% chance that
the average temperature or total precipitation will be in the below normal
class, and N35 means a 35% probability that the average temperature or total
precipitation will be in the near normal class. When EC is specified, all
categories are equally likely.
NOTE - These outlooks are intended for use prior to the start of the valid
periods. Within any valid period, observations and shorter range forecasts
should be consulted. Also, this set of outlooks will be superseded by the
issuances of the new set net month, on Thu Sep 18, 2025.
$$