Tropical Cyclone Herbie

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21 May 1988

Summary

Tropical Cyclone Herbie was an exceptional tropical cyclone for its late occurrence in the year and unusually fast southeastward motion. In fact Herbie is the only cyclone to have ever affected the Australian mainland in the month of May. Herbie caused wind damage between Carnarvon and Denham, produced a storm surge at Denham that left fishing vessels stranded along the main street, grounded a large freighter at Cape Cuvier and caused flooding along the Irwin and Greenough Rivers inundating the streets of Dongara.

Track and Intensity

Herbie developed to the northwest of Cocos Island on 18 May, passing close to the island at 8 am on 19 May as a weak tropical cyclone (category 1) having a central pressure of 990 hPa. Satellite imagery suggested the development of a new low, some 300 km to the south of the original centre on 19 May. This new centre moved rapidly to the southeast and intensified at the expense of the original. Herbie moved some 1500 km in the 24 hours prior to crossing the coast at Shark Bay reaching speeds of over 70 km/h. The central pressure was measured at 980 hPa at landfall. Carnarvon recorded a wind gust of 120 km/h and similar speeds were estimated at Denham. Herbie continued its southeastward track through inland parts of the state and gradually weakened.

Herbie underwent a change in structure as it accelerated into the mid-latitudes known as extra-tropical transition. The regions of dense cloud and heavy rainfall are displaced towards the right quadrants of the system (when looking along the direction of the track) leaving the left quadrants largely free of significant cloud. The strongest winds associated with these fast moving systems occur in the left quadrants where the clockwise rotating winds are augmented by the system's translational speed. The cloud-free squally winds from the north or northeast are a recipe for severe dust storms and an extremely dangerous environment in which fires can engulf the countryside with frightening speed. A schematic of this is shown in figure 2.

Figure 3 (a) and (b) are enhanced infra-red images spaced 24 hours apart showing the 'capture' of Herbie by a cold front well to the south and the elongated cloud streaming to the southeast. The dense cloud and heavy rain denoted by the yellow in figure 3 (b) and on the Carnarvon radar in figure 4, is well southeast of the cyclone centre. The resultant rainfall distribution shown in figure 5 shows the rainfall located south of the cyclone track.

Figure 1. Track of Herbie (click to enlarge).

Figure 2. Schematic diagram showing features of a tropical cyclone undergoing extra-tropical transition

Figure 3. Enhanced infra-red satellite imagery showing Herbie as it moved from the tropics to Shark Bay;

(GMS images courtesy of Japan Meteorological Agency).

(a) 8am 20 May

(b) 8 am 21 May

Figure 4. Radar image at Carnarvon.

Impact

Herbie caused structural damage along the coastal strip from Carnarvon to Denham, extensive damage to banana plantations at Carnarvon, and the grounding of a 30 000 ton freighter, the Korean Star, near Cape Cuvier (photo 1). A 2 m storm surge occurred at Denham, inundating the foreshore. Several fishing vessels were left stranded along the main street when water levels subsided. As Herbie moved inland, severe duststorms occurred on its northern side, while by contrast rainfall totals greater than 100 mm caused flooding over areas south of the track. The Greenough and Irwin Rivers burst their banks flooding houses, especially in Dongara.

Figure 5. Rainfall distribution from Herbie.

Damage Photo

Photo 1. The wreckage of the Korean Star at Cape Cuvier, north of Carnarvon.

Photo reproduced courtesy of The West Australian.