Sydney's Weekend Washout!

It has been raining non-stop in Sydney this weekend with massive rain totals recorded between the Hunter and South coasts over the last 2 days. So where is this deluge coming from and when will it stop?!

Well, the atmosphere is completed saturated and when it's like this all it needs is a "trigger" for a heavy downpour. In this case, the "trigger" is a small-scale low pressure trough that formed off the NSW coast. The very moist air has been feeding into this trough causing widespread torrential rain in Sydney, the Hunter, South Coast and Illawarra. With so much heavy rain falling over a short time period, flash flooding is likely.

Over the last 48 hours, the heaviest falls have generally been in coastal suburbs, closest to this trough. In 24 hours to 9am Sunday morning, we've seen widespread falls of over 100mm with as much as 166mm in Little Bay, it's heaviest March rain since 1975. Other notable falls include:

Avalon- 139mm
St Ives- 179mm
Turrumurra- 175mm
Belrose- 137mm
North Manly-130mm
Sydney Airport- 100mm

Further south, Albion Park recorded 137mm, Wollongong 129mm and Barrengarry 210mm!! The rain has been lighter further west with up to 50mm in the Warragamba catchment area. Considering how dry it has been, this is unlikely to lead to any significant rises.

So- what next? Heavy rain will continue during Sunday, easing later as the trough moves away. But heavy rain is likely to return on Monday as another low pressure trough comes in from the west. The wet weather should start to ease on Tuesday.

Cyclone season ramps up with monster Yasi on the way

Anthony hits QLD coast
TC Anthony hit the coast around Bowen on Sunday night and has since weakened into a tropical low. Anthony delivered damaging wind gusts of 124kmh to Hamilton Island and heavy rain to areas directly south of the cyclone around Mackay with widespread falls of 100-300mm. This has lead to minor-major flooding in the Pioneer catchment. This system is moving in a south-westerly direction and continuing to bring rain to inland QLD.

The monster TC Yasi is next…
But a much larger and powerful TC Yasi is now threatening QLD as not only is it expected to be stronger than Anthony, but it is also a lot bigger meaning that its impact will be much more widespread across QLD. If you look at the satellite image above captured from http://www.weatherchannel.com.au the now ex-TC Anthony is the circular cloud near Townsville, and TC Yasi is the monster to the right spiralling near Vanuatu. It dwarfs Anthony in size and could reach category 4 status as it approaches the QLD coast. A category 4 cyclone is a Severe Tropical Cylone with “very destructive winds” that can gust at 225-279kmh over open flat land. Winds of this strength can destroy and blow away caravans and lead to significant roof loss and structural damage. TC Yasi may weaken as it approaches/crosses the coast due to friction and at this stage its expected to make landfall late Wednesday/Thursday bringing widespread heavy rain and possibly wind gusts of over 200kmh. Since the system is so large its impact will extend across a very large part of the QLD coast. Gale force winds and heavy rain could be felt for 100's of kilometres anywhere north of the sunshine coast.

Is Yasi's path unpredictable?
Contrary to popular belief, not all cyclones are "unpredictable." A TC will respond to the environment around it so if the winds in and around a cyclone are all over the place, a cyclone's path may be erratic and difficult to predict. However if there is a well established direction of environmental flow, the prediction of a cyclone's path can be made with a lot more certainty. In the case of TC Yasi, there is a well established flow of easterly winds so it can be said with some certainty that these winds will carry TC Yasi towards the QLD coast. Since a coastal crossing is still a few days out, it is difficult to predict exactly where TC Yasi will hit.

Where did the name “Yasi” come from?
Various meteorological organisations are responsible for naming TC's depending on where in the world they form, and there are various conventions for TC naming too. TC's that form in Australian waters are named by the Bureau of Meteorology using a set list that runs in alphabetical order. So with Anthony and Bianca most recently forming in our waters, you might be wondering why this TC is called Yasi as opposed to a name starting with "C". Well, since TC Yasi formed out of Australian waters it was named by the Fiji Met Service. They also follow the convention of naming TC's using a set list in alphabetical order, so after naming Ului, Vania and Wilma, Yasi was the next name on the list. When TC Yasi enters our waters it keeps its Fijian name to avoid confusion. The next TC to form in Australian waters will be Carlos.

Double Cyclone Trouble for QLD

---UPDATED AT 6.30AM SUNDAY QLD TIME--- The intensity and movement of cyclones can change rapidly so make sure you check in with the Bureau Of Meteorology regularly for the latest warnings.

The QLD coast is on alert with the prospect of two tropical cyclones making landfall in just the space of a few days.

At 4am local time, TC Anthony was a weak category 1 system and situated approximately 600km ENE of Townsville in the Coral Sea. Anthony is forecast to continue its southwesterly track today and make intensify slightly into a category 2 system as it approaches the QLD coast. A Cyclone Warning continues for coastal and island communities from Lucinda to Proserpine. A Cyclone Watch continues for coastal and island communities from Innisfail to Lucinda and Proserpine to St Lawrence. Damaging wind gusts may develop for coastal and island communities between Lucinda and Prosperpine late Sunday, with Destructive winds gusts near the cyclone centre as it approaches the coast early on Monday morning. Heavy rainfall and local flooding are expected to develop near and to the south of the cyclone, as far south as Sarina, as it approaches the coast some time overnight Sunday.

There is also a low to the north of Fiji that is forecast to develop into a tropical cyclone and move into the region on Tuesday. This system may also impact the QLD coast. There are some indications that this system could be a lot stronger than Anthony, but considering the system hasn't formed into a cyclone yet, it is too early to be certain of this system's intensity or movements.

Why is this tropical cyclone season so active?
One of the strongest La Nina's on record continues to influence the climate of the Pacific Basin. Apart from contributing to above average rainfall across northern and eastern Australia (which has already been experienced in unprecedented amounts leading to record flooding), La Nina events are also characterised by a higher than normal number of tropical cyclones during the tropical season from November to April.

Another climate pattern that influences tropical cyclone activity in the Australian region is the Madden-Julian Oscillation. It is currently out of the Australian region but it may return in the middle of February and this could increase the tropical cyclone potential at this time.

Cyclone season taking off!!

----URGENT UPDATE - TROPICAL CYCLONE BIANCA HEADING TO PERTH----

We're in the guts of the official Australian cyclone season, and so far we've had 7 tropical cyclones in Australian waters with the most recent being Bianca off the WA coast. Cyclones Vania and Wilma didn't make the count since they were officially out of Australian waters but they impacted our eastern seaboard with powerful swell.

This week is particularly active in Australian waters with three systems that I'm watching closely:

----A dramatic change in the movement and intensity of Bianca is expected. See below----

Bianca formed early on Australia Day, reaching Severe Tropical Cyclone status on Thursday 27th January when it became a category 3 system. Bianca now lies off the WA coast and continues to move in a south-westerly direction away from the coast. Bianca is forecast to gradually weaken as it takes up a southerly track overnight on Friday, changing to a south-easterly direction on Saturday. Early on Sunday Bianca is expected to reach the southwest corner of WA and could maintain Tropical Cyclone strength as it makes landfall. If this situation eventuates, damaging winds up to 120km/h may occur between Jurien Bay and Albany. Ocean conditions will also become dangerous. A cyclone watch is currently in effect for this region.

Anthony has re-developed into a Categoty 1 Tropical Cyclone and is situated in the central Coral Sea. It's expected to take a more N/NW track and could make a coastal crossing between Mackay and Cooktown late Sunday/early Monday.

Wilma is a category 3 Severe Tropical Cyclone well offshore near Norfolk Island and will only have a an indirect impact on Australia in terms of generating powerful swell to the eastern seaboard this weekend. Waves won't necessarily be massive but the swell will be powerful and energetic making for dangerous surf, beach and fishing conditions.

Crazy Sea Fog blankets Bondi on Australia Day!

With a forecast of 42 degrees in Sydney's west and 33 degrees for the city today, you'd be forgiven for thinking that it's a perfect beach day for enjoying Australia Day! Afterall, it's set to be the city's hottest Australia Day in 31 years and Penrith's hottest day all summer!

But while it's turning out to be an absolute scorcher, the hot tropical airmass that's causing all of this heat has also contributed to a strange thick sea fog across some of Sydney's most popular beaches, on what is arguably one of Sydney's most popular beach days of the year!

So how has this sea fog formed?
Well, sea fog is also known as "advection fog" which refers to the movement of warmer air over a cooler surface. The hot airmass which is being drawn in from the tropics to Sydney today by northerly winds (and causing Darwin-like humidity!) has been carried over the cooler waters of our beaches. Now the contact of this hot and humid airmass with the colder water has caused the air directly above the sea surface to cool. Cooling of the air causes the water vapour in the air to condense into liquid droplets which we see as fog! It also helps that the winds are light so there's nothing to push the fog away.

When will it go away?
Later today when the sea breeze develops winds will tend N/NE'ly blowing the fog parallel to the coast, so visibilty should improve. Winds will also become stronger which should enhance mixing of the lower atmosphere, helping to dissipate some of this fog, although it could remain hazy. We have a southerly change coming in this evening which will bring a "relatively" cooler and drier airmass through Sydney so sea fog is less likely tomorrow. I say "relatively" because this southerly won't bring much of a temperature drop to Sydney tomorrow. It's not until Friday that temperatures will become more bearable with a forecast 25 degrees for the city and 27 degrees for Penrith.

Sydney- get ready to shiver in the water this weekend!

The summer-like weather is continuing for Sydneysiders for the best part of the weekend but before you dive straight into the ocean to cool off, be prepared for some icy ocean temperatures! Saturday will bring another great beach day with 27 degrees for the coast and a balmy 31 degrees in the west. There’s a slight chance of afternoon storms in the west but beaches should remain dry. But while it’s simmering outside, the ocean may feel like an ice bucket as sea surface temperatures take a dive over the next few days! You’ll need a wetsuit to swim at Bateman’s Bay on the NSW South Coast where the ocean temperature has already dropped from 19 degrees to a chilly 14.9 degrees this week! And the cooling is starting to show in Sydney’s waters which are sitting at 19.4 degress right now and falling. Note that Sydney’s ocean temperature is taken offshore so it’s probably even colder than that.

Why is the ocean so chilly? The cold ocean temperatures are a result of “upwelling.” Basically we’re seeing a consistent stream on north-easterly winds along the Sydney and South Coast which actually work to drag the surface water away from the coast. When this water gets dragged away something has to replace it, so the colder bottom ocean waters rise to the top resulting in a rapid cooling of sea surface temperatures on our coastline. Next week we’ll get southerly winds coming in which should allow sea surface temperatures to warm up again.

Sunday will start off well in Sydney with a high of 25-27 degrees before widespread rain and possible storms develop in the afternoon. Try and make the most of the sunny skies until then as once the rain rolls in on Sunday it will persist right through into next week.

Another spring soaking heading straight for eastern Australia this weekend

The year 2010 has been nothing short of extraordinary when it comes to rainfall, with rain records smashed across much of northern and eastern Australia. The August to October period this year has been our wettest on record (from 111 years of record keeping) across the entire country- and there is another big soaking on the way this weekend. This will be the fourth, widespread, soaking deluge across eastern Australia this spring.

Thanks to a moderate to strong La Nina which is well established in the Pacific Ocean, we have very warm waters off the northern Australian coastline- this is the moisture source for all the rain that we’ve been seeing through northern and eastern Australia in recent months. This week northerly winds across the east have been funnelling very warm and humid conditions across the region so the moisture source for widespread heavy rain is back- all that’s needed now is a trigger! Tomorrow, this trigger comes in the form of a cold front. So the warm and moist tropical airmass from the north will clash with this colder airmass coming up from the south, resulting in an extensive area of rain that will move slowly eastwards. Far eastern SA, western QLD, central and northern VIC and much of NSW could see 50mm of rainfall from this system. Isolated falls of 100mm are also possible which could renew flood warnings across many already saturated catchments.

Of the capital cities, it’s Adelaide and Melbourne that will bear the brunt of this rain event over the weekend. Adelaide will experience a big temperature drop on Friday going from around 30 degrees in the morning to 20 degrees in the afternoon, accompanied by rain. The weather rollercoaster is also heading to Melbourne with the temperature dropping from 32 degrees on Friday to 23 degrees on Saturday. Rain and storms will develop during Friday afternoon and evening with the heaviest day of rain on Saturday. Melbourne could pick up around 50mm from this system.