Prognostic Discussion for Long-Lead Hawaiian Outlooks NWS Climate Prediction Center College Park MD 830AM EST Thu Mar 18 2021 MONTHLY FORECAST DISCUSSION VALID APRIL 2021 Positive sea surface temperature (SST) anomalies from zero degree to one half degree Celsius were observed over Kauai, Oahu and Maui, while zero to negative one half degree Celsius SST anomalies were over the Big island during the previous week. For January through February 2021, rainfall total accumulations were: - Lihue Airport 5.78 inches (84 percent of normal) - Honolulu Airport 4.77 inches (111 percent of normal) - Kahului Airport 4.28 Inches (90 percent of normal) - Hilo Airport 30.60 Inches (163 percent of normal) The NCEP Climate Forecast System (CFS) and other climate models of the North American Multi-Model Ensemble (NMME) predict above average SSTs around the Hawaiian Islands through April 2021. This elevates the chances of near to above normal monthly mean air temperatures for Hawaii in April 2021. Most dynamical models indicate an increased chance of above normal precipitation over the Hawaiian Islands during April 2021. TEMPERATURE PRECIPITATION FCST AVE LIM FCST BLW MEDIAN ABV Hilo EC 72.6 0.7 A60 7.4 8.9 11.2 Kahului A50 74.1 0.6 A60 0.5 0.9 1.3 Honolulu A60 76.3 0.5 A60 0.3 0.5 0.7 Lihue A60 74.0 0.6 A60 1.6 1.9 2.8 SEASONAL FORECAST DISCUSSION VALID AMJ 2021 - AMJ 2022 Refer to the prognostic discussion of the long-lead seasonal outlooks for the CONUS and Alaska for a description of the ENSO outlook and other climate conditions relevant to the seasonal outlook. The observed tropical Pacific atmosphere and ocean conditions are consistent with the ongoing La Nina, with below average sea surface temperatures (SSTs) from the west-central to approximately 110 W longitude in the eastern equatorial Pacific Ocean. Negative subsurface temperature anomalies have weakened and extend from ~100m to the surface in the central and eastern equatorial Pacific Ocean. Tropical convection is suppressed from the west-central to central Pacific Ocean. Low-level easterly wind anomalies were observed over the central and western Pacific Ocean, while upper-level westerly wind anomalies were observed over the central and east-central equatorial Pacific Ocean. There is an approximated probability of 60 percent for the chance of a transition from La Nina to ENSO-Neutral in AMJ 2021. Enhanced probabilities for above normal temperatures are indicated over Hilo in AMJ 2021, over Kahului from AMJ to MJJ 2021, and over the northwestern islands (Honolulu and Lihue) from AMJ 2021 to JAS 2021, while below normal temperatures are forecast over Hilo from JJA to JAS 2021, and over Kahului in JAS 2021, supported by most dynamical and statistical forecast tools. Climate forcing signals, including ENSO, weaken at longer leads, such that Equal Chances (EC) for above, near or below normal temperatures are indicated for Hawaii in ASO 2021 and thereafter. Most dynamical models predict likely above normal precipitation over the northwestern islands (Honolulu and Lihue) in AMJ 2021, while below normal precipitation is favored over Hilo and Kahului from MJJ to JJA 2021, and over Honolulu and Lihue in JJA 2021. Due to considerable uncertainty in the precipitation forecasts from dynamical and statistical models over the Hawaiian Islands in JAS 2021 and longer leads, equal chances (EC) for above, near or below normal precipitation are indicated. Hilo TEMPERATURE PRECIPITATION FCST AVE LIM FCST BLW MEDIAN ABV AMJ 2021 A40 72.9 0.5 EC 21.4 23.7 29.0 MJJ 2021 EC 74.0 0.4 B40 20.2 27.5 29.1 JJA 2021 B40 75.2 0.4 B40 19.4 27.2 31.4 JAS 2021 B40 76.1 0.4 EC 25.2 28.6 33.4 ASO 2021 EC 76.4 0.4 EC 26.1 28.8 33.3 SON 2021 EC 76.2 0.4 EC 24.3 30.2 40.8 OND 2021 EC 75.5 0.4 EC 28.3 34.5 42.0 NDJ 2021 EC 74.2 0.4 EC 26.4 36.6 43.0 DJF 2022 EC 72.8 0.4 EC 19.6 30.2 33.3 JFM 2022 EC 71.8 0.4 EC 22.0 32.0 44.5 FMA 2022 EC 71.7 0.4 EC 24.6 34.1 45.5 MAM 2022 EC 72.0 0.5 EC 22.5 28.4 34.0 AMJ 2022 EC 72.9 0.5 EC 21.4 23.7 29.0 Kahului TEMPERATURE PRECIPITATION FCST AVE LIM FCST BLW MEDIAN ABV AMJ 2021 A45 74.3 0.5 EC 1.2 1.6 2.2 MJJ 2021 A40 76.0 0.5 B40 0.7 1.1 1.8 JJA 2021 EC 77.7 0.4 B40 0.7 1.1 1.5 JAS 2021 B40 79.0 0.4 EC 0.8 1.1 1.6 ASO 2021 EC 79.4 0.4 EC 0.8 1.6 2.5 SON 2021 EC 79.1 0.4 EC 2.1 3.3 4.8 OND 2021 EC 77.8 0.4 EC 4.2 5.3 8.1 NDJ 2021 EC 75.9 0.4 EC 5.2 7.6 9.5 DJF 2022 EC 73.8 0.4 EC 4.6 6.9 8.7 JFM 2022 EC 72.5 0.4 EC 4.2 6.2 8.2 FMA 2022 EC 72.3 0.4 EC 3.2 4.1 6.4 MAM 2022 EC 73.0 0.4 EC 2.5 3.5 4.6 AMJ 2022 EC 74.3 0.5 EC 1.2 1.6 2.2 Honolulu TEMPERATURE PRECIPITATION FCST AVE LIM FCST BLW MEDIAN ABV AMJ 2021 A60 76.3 0.4 A40 1.2 1.6 1.8 MJJ 2021 A55 78.2 0.4 EC 0.8 1.4 1.6 JJA 2021 A50 79.9 0.4 B40 0.7 0.8 1.3 JAS 2021 A40 81.3 0.4 EC 1.0 1.4 1.7 ASO 2021 EC 81.7 0.4 EC 1.6 2.4 3.1 SON 2021 EC 81.4 0.4 EC 2.5 4.0 5.6 OND 2021 EC 80.0 0.4 EC 4.4 6.4 8.5 NDJ 2021 EC 77.7 0.5 EC 3.9 5.6 8.8 DJF 2022 EC 75.3 0.5 EC 3.7 5.6 8.6 JFM 2022 EC 73.9 0.4 EC 2.1 4.6 7.8 FMA 2022 EC 73.8 0.4 EC 1.9 3.2 4.7 MAM 2022 EC 74.8 0.4 EC 1.8 2.6 3.0 AMJ 2022 EC 76.3 0.4 EC 1.2 1.6 1.8 Lihue TEMPERATURE PRECIPITATION FCST AVE LIM FCST BLW MEDIAN ABV AMJ 2021 A65 74.2 0.5 A40 4.7 5.5 6.0 MJJ 2021 A60 76.0 0.5 EC 4.9 5.4 5.9 JJA 2021 A50 77.7 0.4 B40 4.4 5.3 6.9 JAS 2021 A40 79.0 0.3 EC 5.3 6.1 7.8 ASO 2021 EC 79.4 0.3 EC 6.2 7.9 8.4 SON 2021 EC 79.1 0.3 EC 9.2 10.0 11.2 OND 2021 EC 77.8 0.3 EC 9.2 11.7 15.6 NDJ 2021 EC 75.7 0.3 EC 8.6 12.1 16.9 DJF 2022 EC 73.6 0.4 EC 7.5 8.4 14.0 JFM 2022 EC 72.2 0.4 EC 6.5 8.8 13.8 FMA 2022 EC 72.1 0.5 EC 5.8 8.4 9.9 MAM 2022 EC 72.8 0.5 EC 5.3 6.6 8.0 AMJ 2022 EC 74.2 0.5 EC 4.7 5.5 6.0 FORECASTER: Luke He Anomalies are based on the 1981-2010 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 Apr 15, 2021. $$