A Comparison of Three Prolonged Periods of Heavy Rainfall over the Hawaiian Islands

Abstract

The anomalous circulation patterns during an unusually prolonged stormy-weather period in Hawaii from 19 February to 2 April 2006 are analyzed and are compared with those of two previously known prolonged heavy-rainfall periods (March 1951 andFebruary 1979). The circulation patterns for these three periods are characterized by 1) a negative Pacific-North American (PNA) pattern in the midlatitudes with a blocking high southwest of the Aleutian Islands, 2) retraction and splitting of the zonal jet into a polar jet north of 508N and a persistent subtropical jet to the south over the central Pacific Ocean, 3) an anomalous low west of the Hawaiian Islands embedded in the subtropical jet, and 4) a weaker-than-normal Hadley circulation in the mid-Pacific. The moisture advected from low latitudes by the southerly wind component east of the persistent anomalous low, combined with upward motion, provides the large-scale setting for the unusually prolonged unsettled weather across the Hawaiian Islands. For all three cases, the prolonged stormy weather started after the onset of large-scale blocking and a negative PNA pattern over the North Pacific and the occurrence of a persistent anomalous low embedded in the subtropical jet west of the Hawaiian Islands. Furthermore, the persistent low was located at the optimal position to bring moisture from the central equatorial Pacific to Hawaii. The stormy weather ceased after the midlatitude blocking pattern weakened and the anomalous low in the subtropics decayed and/or shifted westward. There are no apparent common precursors in the 2-week period prior to the prolonged stormy weather among these three cases, however. FIG. 4. (a) Mean moisture flux yq (contour interval every 10 g kg 21 m s 21 ) at the 850-hPa level and (b) mean transient moisture flux y9q9 (contour interval every 1 g kg 21 m s 21 ) at the 850-hPa level during

Statistical downscaling of rainfall changes in Hawai‘i based on the CMIP5 global model projections

“…In our downscaled projections, the subtropical zonal dipole pattern constitutes a robust feature in multimodel ensemble projections. Although the dynamical reasons behind these circulation shifts are currently not well understood, an interplay between the position and extension of the Asian jet and subtropical cyclone activity and blocking events might play an important role in the central and eastern Pacific [ Chu , ; Huang et al ., ; Otkin and Martin , ; Jayawardena et al ., ]. Zonally aligned dipole‐like circulation anomaly patterns can be found in various mode decompositions of the atmospheric circulation [ Wallace and Gutzler , ; Barnston and Livezey , ; Johnson and Feldstein , ].…”

Analysis of the initiation of an extreme North Pacific jet retraction using piecewise tendency diagnosis

“…The trough diverted flow southward in the central Pacific, and, in concert with the ridge to its north, enhanced the deformation associated with the jet exit region, now much farther upstream than on 11 February. The development of the subtropical trough also coincided with the beginning of the rainy period over Hawaii (Jayawardena et al, ).…”

“…The North Pacific jet retraction that began in mid‐February 2006 was related to a period of extreme rainfall over Hawaii that continued throughout March (Table 1 JM; Jayawardena et al, ). The Federal Emergency Management Agency (FEMA) declared the event a natural disaster due to the resultant flooding, mudslides and damages (FEMA Case No.1640).…”

“…This study examines the initiation of a jet retraction that occurred from February to March 2006, and led to an unprecedented period of rainfall, flooding and mudslides in Hawaii (Jayawardena et al, ). This retraction was extreme in terms of its persistence and overall reduction in the zonal wind speed, ranking first and third, respectively, in those categories (JM).…”

Evidence for nonlinear processes in fostering a North Pacific jet retraction

“…7), resembling the negative phase of the Pacific-North American teleconnection pattern (Wallace and Gutzler, 1981). While periods of retraction and the attendant wavy (and often blocked) flow are well-known forecast challenges (Renwick and Wallace, 1996;Winters et al, 2019), and are associated with notable sensible weather impacts such as flooding over Hawaii and the west coast of North America as well as extreme cold (Hoskins and Sardeshmukh, 1987;Otkin and Martin, 2004;Jayawardena et al, 2012), a complete understanding of the transition to such a retracted state is lacking in the current literature. Various physical mechanisms for blocking onset and blocking maintenance have been attributed to deformation, vortex-vortex interactions, diabatic heating and tropical convection, but consensus regarding which of these processes is the most important has not yet been achieved (Frederiksen, 1983;Shutts, 1983;Yamazaki and Itoh, 2013;Pfahl et al, 2015;Henderson et al, 2016;Nakamura and Huang 2017).…”