Pacific Science (1989), vol. 43, no. no. 1 © 1989by University of Hawaii Press.Press. All rights reserved Recent Climate History of Hawaii1 DENNIS NULLET 2 ABSTRACT: The recent energy and synoptic climate of Hawaii is examined inin this article. The results indicate trends in the energy climate, climate, increasing tempera­ ture and decreasing solar radiation, though no evidence is found of trends or cycles in the synoptic climatic elements, elements, rainfall and sea level pressure.pressure. THIS ARTICLE PRESENTS a brief discussion and value is one of the highest annual rainfall analysis of the climate in Hawaii since scienti­ totals ever recorded in Honolulu. Mean baro­ fic weather observations began in the nine­ metric pressure was 1015 mb (29.973 (29.973 in. mer­ teenth century. cury) during his stay, near the long-term long-term mean for September through April of 1016 mb. mb. Sea surface temperatures averaged 26.426.4°C°C (79SF), which, if accurate, would be un­ WEATHER OBSERVATIONS usually warm (Wilkes (Wilkes 1851). Some of the earliest meteorological obser- In the late nineteenth century, weather ob- vations in Hawaiiwere reported byLt. Lt. Char- servations became more common asagricul­ les Wilkes, who, while in command ofthe U.S. U.S. tural interests grewgrew,, and finally the newly Exploring Expedition,Expedition, spent the winter of established Climatological Office for the then 1840-18411840-1841 in the islands. islands . Wilkes' visit to the Territory ofHawaii began publishing records islands, just 62 years after their discovery byin 1905.By 1985 nearly 2000 climatological Captain Cook, appears tohave coincided with stations had been established and maintained blustery weather. He found thedaytime winds at one time or another, giving Hawaii one of "blow with great strength" though "the nights the densest climate monitoring networks in are calm and beautiful" (Wilkes 1851). 1851). Wilkes the world (Giambelluca et al. 1986). added a postscript to his assessment of the To illustrate the history of the general eli­cli­ nocturnal weather, however. On an expedi- mate during this century, weather data are tion to the summit of Mauna Loa,Loa, Wilkes' graphed in Figures 1I and 2. 2. The data are party measured 457 mm (18in.) of snow, ex- separated into climatic elements related to the perienced gales from the southwest gusting up energy balance, radiation and temperature, and to 21 m/sec m/sec (47 mph), mph) , and recorded tempera- climate elements that indicate synoptic condi­ turesas low as - 7.8°C (18(1 8°F).°F). On huddling in tions, tions, rainfall and sea level pressure. The air camp near the summit, WilkesWilkes later wrotewrote,, temperature curve was compiled by taking the "the howling wind ... .. rendered the hours of average of three windward sites at Lihue, darkness truly awful" awful" (Wilkes 1970)1970).. Kauai (State ID: ID : 1020.1,1020.1, National Oceanic Wilkes reported the mean annual tempera- and Atmospheric Administration (NOAA) ture at Honolulu to be24.3°C 24.3°C (75.8°F)(75.8°F) based ID: ID: 5580);5580); Hana, Maui (State ID: 355.0; 355.0; --- onon-s-everal-years--of-measuremen-several years "ofmeasurements,"nearts;-n-eactlre- the - NOAAID:1125)N<JAAID:-lt25);1l11d--Hilo;-;·-andHilo;:Hawaii(SHawaii (Statetate long-term mean of23.9of23.9°C.°C. He also listedrain- ID:87.0; NOAA ID: 1492) (all data from fall totals of 536 mm (21.1 in.) during 1837 NOAA's Climatological Data for the States)States).. and 1189 mm (46.8 (46.8 in.)for 1838. The1838 Only windward sites wereused in the tempera- ture curvecurve,, because these sites are less affected by daytime land heating and thus more accu­ rately represent the oceanic oceanic climate.climate . The data 1 Manuscript accepted 10May 1988. 1988. 2 University of Hawaii Hawaii at Manoa, DepartmDepartmentent of Geo­ since 1950 represent airport records adjusted graphygraphy,, HonoluluHonolulu,, Hawaii 9682296822.. to town sites by comparing overlapping per- 96 AM' ,! g. • @i 1·4#tJtl@!@¥ # ?§44ff4Pi g ·#$l¥WW..lffii## ·ii¥!$lEiif1iE&Z£.f444 iJ£WrlfiMh·iW Recent History of Hawaii'sHawaii 's Climate-NuLLETClimate-s-Nutr.sr 97 N o E o ::, 22 00 000 0 0 0 0 ~ c ----------------?~----9_erQ-.--Q~-.--.---.-.--.-~----9_erQ- ---Q~- -----------------------.::-----.-.-. -~---- 0 ----------------? .. -Q9.----------Q9.------------------------0 ------- ~ o 0 U'0 20 00 o0 a:cr:'" 00 1818 o 6. 6. 25 25 6. 6. 6.6. _____ A SeSeaa SurlaceSurface ---------~--".-:>:~>;-A~-"'--~-"'~"'-------------er--t:s.-8---- ~~=::;::~:=:~~---------z,---------t,. 6. '" o 00 o o o o o o o 000o Air 0.•__ 0. 0_ o 0 o 0 o o o 00 o o --------Mean--------Mean 22+----,-----,-----,-----,-----,-----r-----,-------,r--'22 + - - - - ,---- -,----- ,----- ,----- -,----- ,----- ,----- 0' 1905190 5 191519 15 19251925 1935193 5 1945 19551955 19619655 11975975 1985 FIGURE 1.1. Historical energy climate. climate. DataDa ta are discussed in the text. The reciprocal relationship between temperature and radiation may indicate that cloudiness acts as a negative feedback agent to temperature fluctuations in the north­ central Pacific. (0 symbols indicate ggloballoba l radiationradiation and air temperature.temperature. '"6. symbols indicate sea surface temperaturetemperature.).) 1018~1 01 8~ 1017 1016101 6 :0 1015101 5 .§. ~ 1017 :J::J <n ~ 101610 16 0:0- a; 1015101 5 > ~ 1014 11>Q) (/)en'" 11013013 1012-10 12 4500 ----------E"E------------- .§. 3000 'iii 'E"E 'iii-(ij a:cr: 15001500 HonoluluHonolulu O+------r------r-----,-----,-------,-------.-----,..-JO+-----,--------r-----r-----,------.--------.-----,..-J 18801880 189518 95 191019 10 19251925 1940 19551955 197019 70 19851985 FIGURE 2.2. Historical synoptic climate indicators.indicators. Data are discussed in the texttext.. Cycles and trends appear absenabsentt in the data, altalthoughhough rainfall variations are generagenerallylly in phase at the lleeward,eeward, windward, and intermediate sitessites.. 98 PACIFIC SCIENCE, Volume 43, January 1989 iods.iods. Accordingly, the following corrections however. Infact, 18001800-1850-1850 was a time of were applied to the post-1950 airport records:records : maxima in AAlpinelpine glaciation and Icelandic sea Lihue: -0.6°C, - 0.6°C, Hana: -0.2°C,- 0.2°C, Hilo, ++0.1°C.0.1"C. ice (Lamb 1977). Possible sources of variation in these records The cause ofthe temperature trend is largelarge­­ are discussed discussed by Hoyt and Siquig (1982). The ly a matter of speculationspeculation.. Possible explanaexplana­­ sea surfacesurface temperaturetemperature (SST) curve has been tions might be a change in atmospheric circu­ derived from weekly sea surfacesurface temperature lation or warming by greenhouse gases, such measurements collected offKoko Head, Oahu.Oahu. as carbon dioxide and methanemethane.. Wentworth These data are discussed in Seckel and Young (1949) reported a significant easterly shift ill"in (1977).(1977). Solar radiationradiation has been measured measured in the tradewinds over Hawaiian waters between Honolulu since 1932, 1932, first at the Hawaiian 1910 and1940 followed by a return to more Sugar Planters'Planters' Association's Makaki Substa­ northerly winds through 1946,corresponding tiontion (StateID: ID:707.0), 707.0), and, since 1976, at the nicely to the temperature curvecurve.. An analysis of University ofHawaii (these data are discussed local winds since 1946 shows no continuation by Ekern 1982). 1982). The rainfall data (from of this trend, but a study of winds over the Lihue,Lihue, Hilo, and Honolulu;Honolulu; State ID: 703.0; 703.0; entire Pacific Ocean (Whysall et al. 1987)indi­1987) indi­ NOAA ID: 1919) and sea level pressure data cates a slight easterly shift in the tradewinds (from(from Honolulu) have been smoothed by cal­ over thepast 30years. years. An easterly shift in the culating 5-year running mean values; that is,is, tradewinds would increase the southerly a value plotted for a given yearyear represents the component of the North Equatorial Current average of that year'syear's measurements plus the and bring warm equatorial water into the twotwo previousand two successive year's year' s mea­ region.region . Seasonalcycles in the North EquaEqua­­ surementssurements (data from NOAA'sNOAA's Climatologi­Climatologi­ torial Current and associated forcing mech­ calcal Data forforthe States and the World Meteo­ anisms are discussed by Wyrtki (1974) and rologicalrological Organization'sOrganization's World Weather White(1977), though no trends are evident Records).Records). The quality of the rainfall datadata are between 1950 and 1970. Namias (1969), how­ discusseddiscussed by Giambelluca et al. (1986). ever, reported warmer than normal SSTs for much of the north-central Pacific between 1954 and 1967. This study also suggests an THE ENERGY ENERGYCLIMATE CLIMATE abrupt increasein SST in the fall of 19611961,, Climatic time series data are generally anal- anal - associatedassociated with an anomalously strong north yzed by looking for trends and cycles cycles in the Pacific high-pressure ridge. This jump corres­ individualindividual climatic elements and for relation-relation- ponds closelywith the temperature data given shipsshipsbetween these elements. elements. An analysis of in Figure 1. I. thethe recentenergy climate depicted in Figure 1IAs another possible mechanism for the obob­­ isis particularly interesting. Air temperatures served warming trend in HawaiiHawaii,, it is particu­ rose from the the beginning of the century until larly appropriate to consconsiderider greenhouse gasgas­­ about 1940,