It’s official – Melbourne has experienced its warmest-ever July day - but the summery burst was shortlived with storms hitting the city.
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Bureau of Meteorology senior forecaster Scott Williams said it was an extraordinary day in Melbourne.
"It was our hottest ever July day at 23.3 degrees (at 2.02pm) - 10 degrees above the July average."
A cold front hit the city just after 3.30pm, with wind gusts of 100km/h recorded at St Kilda at 3.38pm and 102km/h on Port Phillip Bay.
Mr Williams said the temperature dropped almost immediately to 17 degrees and would continue to fall to a low of 12 degrees overnight.
The northern suburbs bore the brunt of the rain, with 20mm falls measured in Craigieburn and Kilmore. The CBD recorded falls of 7mm.
SES spokesman Lachlan Quick said over 300 calls for help had been received, the bulk from Melbourne’s northern and eastern suburbs.
"This is the discovery phase, as people arrive home and find damage," he said.
"We had nearly 40 units out at our peak."
A roof ripped off a garage brought power lines down in Reservoir but nobody was injured in the incident.
Mr Quick said about 150 calls had been received in the metro area but many more call-outs were expected as people returned home to find damage.
"We're receiving about two calls per minute," he said.
"Our busiest unit has been Waverley, then Northcote, Moorabbin and Eltham."
It has also been windy around the state, with peak gusts of 122 km/h recorded at Mt Hotham, 87 km/h at Kilmore, 78 km/h at Tullamarine, 78 km/h at St Kilda, 74 km/h at Essendon, 72 km/h at Laverton and 57 km/h at Frankston.
The Bureau of Meteorology has issued severe weather warnings for most of the state and the SES was expecting large numbers of fallen trees.
"We see a fair bit of damage happening ... 110km/h over a widespread area is a big concern," Mr Quick said earlier. "There’s going to be lots of traffic – school’s back and there’ll be impacts on the roads, there’ll be impacts on the buildings."
Unusually, said Mr Quick, Thursday’s prevailing winds will be northerly rather than westerly. "About a year ago, we had a thousand trees down over a couple of days when we had these high-level northerly winds."
The Alpine areas, including ski resorts, are expected to be hit by gusts of up to 130km/h. "It's not great skiing weather," said Mr Quick.
Thunderstorms and rain are also forecast for Friday.
"Remarkably it's happening in what is the typically the coldest week of the year," said David Jones, head of climate analysis at the Bureau of Meteorology.
The temperature, if taken in the last week of the month, would be closer to 24.5 or 25 degrees, he said.
The Melbourne peak "is another unprecedented high temperature event," Dr Jones said, adding to a national pattern of hot spells every six weeks or so since November last year.
Nationally, Australia's mean temperatures are running almost 2 degrees warmer than average, placing the month on course to be one of the hottest Julys on record, he said.
The warmth is not confined to Victoria, with Sydney remaining on course for five days over 20 degrees or warmer conditions – the first such sequence in July since 1928. Wednesday was the city's warmest July day in four years at 24.3 degrees, with 22.6 degrees today and 21 tipped for Friday before a cold front arrives.
Several factors are at play in the heatwave wave, Dr Jones said: "The Australian continent is surrounded by record high ocean temperatures, we know global temperatures are running at near-record highs, and when we see a lack of rain and northerly winds across Australia, we’re getting these spikes in temperatures."
Melbourne will only receive up to 15 millimetres on Thursday and 7 millimetres on Friday, said Mr Missen, but the state's north-east could get between 60 to 90 millimetres over the two days.
The SES are making preparations for flash flooding and thunderstorm damage, said Mr Quick. "The warm air we've got at the moment is about to get hit by a whole lot of cold air and that means we’ll have some pretty decent thunderstorms," he said.
"The wind and the thunderstorms are what we'll keep our eye on the most ... the rainfall is probably less of a problem."
Mark Cattell, Victoria SES State Commander, said preparation was the key to defend against property damage or injury caused by high winds and violent thunderstorms.
"Our volunteers and staff are on standby across the state and we are monitoring the situation closely," he said.
"Flash flooding can happen without warning and become dangerous very quickly, so it's important to prepare ahead of time and have a plan.
"Simple precautions include checking gutters and downpipes for blockages, securing outdoor furniture and objects and having an emergency plan for your home, family and business.
"Don't shelter under a tree during a thunderstorm, and if you can help it don’t park your car under one either - you could be in for a nasty surprise in the morning."
With Peter Hannam and Jessica Wright
MELBOURNE'S MIDWINTER HEATWAVE
- Record: July maximum 23.3
- Reported: 2.02pm Thursday
- Previous record: 23.1C, July 31, 1975
- Warmest ever start to year
- Maximum average: 22.5C for 2013.
