TC STEVE (14P) PART #3 - TOP END and WESTERN AUSTRALIA - REPORT

2nd March to 10th March 2000

By Carl Smith


carls@ace-net.com.au


Note: see TC STEVE (14P) PART #1 - DIRECT HIT ON CAIRNS - REPORT for the first incarnation and TC STEVE (14P) PART #2 - GULF OF CARPENTARIA - REPORT for the second incarnation of this rather unusual cyclone.

REPORT

TC STEVE formed over the Coral Sea, made a direct hit on Cairns, degenerated to a tropical low as it crossed southern Cape York Peninsula, regenerated to a tropical cyclone again in the SW Gulf of Carpentaria, and degenerated to a tropical low again over the southern 'Top End' of the Northern Territory.

At 8:00 am CST [6:30 am WST] Thursday 2 March 2000 [012230 UTC], the Darwin Bureau of Meteorology (BoM) Tropical Cyclone Warning Centre issued Tropical Cyclone Advice (TCA) #1 saying a CYCLONE WATCH has been issued for coastal and island communities between Cape Fourcroy and Kalumbaru in Western Australia, including Darwin. At 8am CST [6.30am WST] a TROPICAL LOW [ex-Steve] Central Pressure (CP) 996 hectoPascals (hPa = MB) with wind gusts near centre of 60 kilometres per hour (km/hr) (30 knots = KT) was located near 14.7 S 133.4 E, over the Top End, about 100 kilometers (km) (55 nautical miles = NM) E of Katherine, moving WNW at 15 km/hr (8 KT). There is a possibility of a cyclone developing during Friday afternoon as it moves across the coast into the Timor Sea. GALES are not expected in coastal areas within the next 24 hours, but may develop in the next 24 to 48 hours.

The WATCH was upgraded to a WARNING in TCA#3 issued by the BoM at 5:00 pm CST [3:30 pm WST] [020730UTC] saying a CYCLONE WARNING has been declared for coastal and island communities between DARWIN in the Northern Territory and KALUMBURU in Western Australia. A CYCLONE WATCH extends W to COCKATOO ISLAND in Western Australia. The CYCLONE WATCH between CAPE FOURCROY and DARWIN has been cancelled. At 5.00 pm CST [3.30 pm WST] a tropical low [ex-Steve] CP 996 hPa was located near 14.8 S 132.2 E over the TOP END, about 40 km (22 NM) SSW of KATHERINE and 300 km (160 NM) SSE of DARWIN, moving W at 15 km/hr (8 KT). It is expected to cross the coast near Port Keats on Friday morning. There is the possibility of a cyclone developing during Friday afternoon as the tropical low moves over the Joseph Bonaparte Gulf. GALES with gusts to 100 km/hr (55 KT) may develop along the coast between DARWIN and KALUMBURU during Friday. STRONG WINDS with squalls to 90 km/hr (50 KT) are currently being experienced over the Top End.

JTWC began issuing warnings again at 022100UTC with Tropical Cyclone 14P warning #09 saying that at 021800Z it was near 14.6S 130.4E moving 285 degrees at 8 knots with maximum sustained winds of 25 KT and gusts to 35 KT, and forecast a regeneration as it approached the coast.

Subsequent warnings showed that it moved W then WSW, emerging briefly over water as indicated in TCA#9 saying a CYCLONE WARNING is now current for coastal and island communities between DALY MOUTH in the Northern Territory and COCKATOO ISLAND in Western Australia. The CYCLONE WARNING between DARWIN and DALY MOUTH has been cancelled. A CYCLONE WATCH extends west to BROOME in Western Australia. At 11.00 am CST [9.30 am WST] Friday 3 March 2000 [030130UTC] a tropical low [ex-Steve] CP 995 hPa was re-located near 14.9 S 129.3 E over the southern Joseph Bonaparte Gulf, 80 km (45 NM) SSW of Port Keats and 145 km (80 NM) ENE of Wyndham, moving WSW at 20 km/hr (11 KT). The centre of the low is now expected to remain close to the Joseph Bonaparte Gulf coast during the morning, and then track westwards across the Kimberley tonight. The low is now considered unlikely to develop into a tropical cyclone today but there is a chance the low may redevelop into a cyclone tomorrow when it moves off the west Kimberley coast. GALES with gusts to 120 km/hr (65 KT) may develop along the coast between DALY MOUTH and COCKATOO ISLAND later today or early tomorrow. STRONG WINDS with squalls to 90 km/hr (50 KT) are currently being experienced over the southwestern Top End and north Kimberley coast.

It continued on it's WSW path overland across the Kimberleys, and responsibility was handed from BoM Darwin to BoM Perth for TCA#11 issued at 6:55 pm WST on Friday, 3 March 2000 [031055UTC], and it emerged on the coast 30 km (16 NM) N of Broome at 1:00 am WST on Sunday 5 March [041700UTC] with CP of 992 hPa and wind gusts below 100 km/hr (55 KT), and JTWC noted that at 042100UTC it was located over the Dampier Land coast and that Broome radar indicated convection was confined to the periphery of the system and that moderate/heavy precipitation extended from Pender Bay SE to Derby then SW across Dampier Land to the coast near Broome.

The low remained close to the coast inhibiting development, and was once again named Tropical Cyclone Steve in a shipping warning saying that at Noon WST on the 5th of March [050400UTC] it had a CP 988 hPa and was at 18.4S 120.4E moving SW at 10 knots with 30/45 knot winds within 120 NM of the centre.

TC STEVE was the first system to become a named cyclone by each of the 3 Australian Tropical Cyclone Warning Centres first from Brisbane, then Darwin, and finally Perth.

In the remarks section of the JTWC warning no 20 issued at 051500UTC it was noted that it was located about 80 NM ENE of Port Hedland tracking WSW at 09 KT with current intensity estimates of 45 and 55 KT. Animated infrared satellite imagery showed that deep convection was continuing to organise and wrap around the Low Level Circulation Centre (LLCC) over the past 6 hours, with improving outflow over the system. UW-CIMSS analysis shows that an upper-level anti-cyclone had begun to develop over the LLCC, and it was under weak vertical wind shear. Port Hedland radar showed that convection had increased in areal coverage.

Steve continued moving slowly WSW near the Pilbara coast, which inhibited development, with only a gradual increase in intensity, becoming Cat 2 at 3am WST 6th [051900UTC] when it was located near 19.4S 118.6 E, anout 100 km (55 NM) N of Port Hedland and 235 km (125 NM) NE of Karratha, with CP 980 hPa and maximum wind gusts to 125 km/hr (65 KT). The cyclone had resumed a steady WSW track at 15 km/hr (8 KT).

Over the next few hours, Steve deepened to be 975 hPa gusting to 140 km/hr (75 KT) at 6am WST [052200UTC] and 150 km/hr (80 KT) at 10 am WST [060200UTC]. During the day it maintained this intensity moved slowly to be 40 km (22NM) NNW of Karratha at 3pm [060700UTC].

It remained stationary 50 km (27 NM) NW of Karratha from 4pm WST [060800UTC] to 7pm [061100UTC] before resuming WSW movement. In their remarks at 060900, JTWC noted that animated multi-spectral satellite imagery showed that TC 14P had continued to strengthen and had developed a 105 NM diameter Central Dense Overcast (CDO), and that animated radar imagery from Port Hedland showed that the strongest convection was S through NW of the LLCC.

TC Steve crossed the coast at about 2 am on the 7th of March [061800UTC] as Category 2 975 hPa with maximum wind gusts to 150 km/hr (80 KT) near 21.3 S 115.7E about 135 km (75 NM) WSW of Karratha and 70 km (40 NM) ENE of Onslow and was moving SW at 13 km/hr (7 KT). JTWC noted in their remarks at 061500UTC that animated infrared imagery showed that it had maintained intensity over the last 6 hours and the LLCC was embedded about 45 NM into the convection, with animated radar imagery from Port Hedland depicting an inner core of convection straddling the coast near Dampier with the majority of the convection over water.

TC Steve weakened as it moved overland, being Cat 1 980 hPa with gusts to 90 km/hr (50 KT) at 6am [062200UTC] near 21.8 S 115.3 E about 200 km (110 NM) SW of Karratha and 25 km (14 NM) SE of Onslow and was moving SW at 16 km/hr (9 KT).

It began showing signs of reintensifying at 10 am [070200UTC] when wind gusts had increased to 100 km/hr (55 KT) and it was near 22.5 S 115.0 E about 95 km (50 NM) S of Onslow and 110 km (60 NM) ESE of Exmouth moving SSW at 20 km/hr (11 KT), however it maintained this intensity and was emerging into the Indian Ocean at 10pm [071400UTC] when it was near 23.2 S 113.8 E about 10 km (5 NM) SSE of Coral Bay, 145 km (80 NM) SSW of Exmouth and 190 km (105 NM) N of Carnarvon and moving WSW at 10 km/hr (5 KT). JTWC noted in their remarks at 071500UTC that animated imagery showed that it had begun to move offshore into the Indian Ocean and that animated water vapour imagery continued to indicate good outflow aloft.

It moved slowly over the next few hours and had intensified to 120 km/hr (65 KT) by 7am on the 8th of March [072300UTC] when it was near 23.6 S 113.6 E about 50 km (27 NM) SSW of Coral Bay, 170 km SSW of Exmouth and 150 km (90 NM) N of Carnarvon and was moving SSW at 4 km/hr (2 KT).

At 4pm [080800UTC] it was near 24.9 S 113.2 E about 45 km (25 NM) W of Carnarvon and 120 km (65 NM) NNW of Denham and was moving SSW at 15 km/hr (8 KT), and by 7pm [081100UTC] it had stalled near 25.0 S 113.1 E about 60 km (30 NM) WSW of Carnarvon and 110 km (60 NM) NNW of Denham. In their remarks at 080900UTC JTWC noted that animated satellite imagery showed that convection had begun to shear off to the E, and that animated radar imagery from Dampier showed that the LLCC was near the tip of Cape Ronsard in the Geographe Channel, with animated water vapour imagery continuing to indicate good outflow aloft.

Over the following hours it drifted slowly S, and by 4 am on the 9th of March [082000UTC], had began to lose intensity with wind gusts to 100 km/hr (55 KT) when it was near 25.3 S 113.3 E about 60 km (30 NM) SW of Carnarvon and 70 km (40 NM) NNW of Denham moving S at 8 km/hr (4 KT). In their remarks at 081500UTC JTWC noted that animated satellite imagery showed the convection had begun to weaken and it had become more disorganised, and animated radar imagery from Carnarvon showed the LLCC was situated over the northern end of Bernier Island.

By 10 am [090200UTC] it had weakened to 90 km/hr (50 KT) and was near 25.4 S 113.6 E about 60 km (30 NM) S of Carnarvon and 60 km (30 NM) N of Denham moving ESE 10 km/hr (5 KT). In their remarks at 090300UTC JTWC noted that animated satellite imagery depicted deep convection remaining over the LLCC which had weakened significantly, and that the latest Carnarvon radar image showed significant weakening of the heavy precipitation S of the system, and moderate precipitation is confined to an area over Shark Bay near the LLCC. Mid-level analysis reveals it has remained within a weakness in the subtropical ridge, and it has begun o turn more ESE with the apprach of a short wave trough associated with a frontal system moving towards SW Australia.

At 1pm [090500UTC] the BoM cancelled the cyclone warnings as intensity had dropped below category 1, CP 982 hPa with maximum wind gusts to 70 km/hr (40 KT), and ex-TC Steve was near 25.6 S 113.8 E about 80 km (45 NM) S of Carnarvon and 45 km (25 NM) NE of Denham, and was expected to cross the coast in Shark Bay during the afternoon.

JTWC continued issuing warnings, noting in the remarks at 091500UTC that it was near 26.1 S 114.4 E and had intensified slightly and made landfall near Hamelin at 091130UTC and had tracked SW at 3 KT during the past 6 hours, with current satellite intensity estimates of 35 and 45 KT. Animated infrared imagery showed that the convection had strengthened slightly over the past 6 hours, and imagery depicted a 90 NM symmetric area of convection centred over the LLCC. The latestCarnarvon radar image showed that the majority of convection was now overland E and S of the LLCC, and a 091027UTC Special Sensor Microwave Imager pass depicted a relatively small area of deep convection near the LLCC with a large area displaced about 120 NM S of the LLCC.

In the JTWC remarks at 100300UTC it was near 27.2 S 116.4 E about 97 NM ESE of Hamelin and had tracked ESE at 10 KT for the last 6 hours, with current satellite intensity estimates of 35 KT. Animated infrared and multispectral imagery depicted that the deep convection had been persistant and has remained over the LLCC even though it had been tracking over land during the past 12 hours. The LLCC appeared to be closer to the western edge of the convection than 6 hours ago indicating an increasing westerly wind shear.

In the remarks of the final JTWC warning it was noted that at 101500UTC it was near 29.6 S 119.7 E about 220 NM E of Geraldton and had tracked SE at 17 KT during the past 6 hours. Current satellite intensity estimates of 25 KT and animated infrared imagery depicted a rapidly weakening system with deep convection decreasing in areal coverage during the past 12 hours, and indicated it had a partially exposed LLCC and was under strong westerly wind shear. It was forecast to continue to track SE over SW Australia and dissapate as a significant tropical cyclone by the end of the period, to be near 31.2 S 122.2 E at 110000 UTC.

END REPORT.

NOTES:

Note 1: Tropical Cyclone Advices, Updates, and Shipping Warnings used as sources for meteorological information in this report were issued by the Australian Bureau of Meteorology (BoM) Darwin and Perth Tropical Cyclone Warning Centres and are Copyright Commonwealth of Australia 1999, Bureau of Meteorology - http://www.bom.gov.au. BoM information is used unless otherwise noted.

Note 2: The BoM issues warnings to the Australian public using kilometers for distances, kilometers per hour for maximum gust wind speeds, hPa for central pressure, and times are CST, which is Australian Central Standard Time = UTC + 9.5 hours, or WST, which is Australian Western Standard Time = UTC + 8 hours. I have converted all these and added in them brackets, so changing to nautical miles (nearest 5 NM), knots (nearest 5 KT), hPa = MB, and times are also given in UTC.

Note 3: Joint Typhoon Warning Center (JTWC), Pearl Harbour, tropical cyclone warnings were also used for extra meteorological information where indicated, and that material is copyright JTWC - http://www.npmoc.navy.mil/jtwc.htm.

END REPORT


Maintained by Carl Smith.
carls@ace-net.com.au

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