MODELS AND RAINFALL - INTENSE RAINFALL IS LIKELY OVER THE EAST COAST AND UP NORTH - A WET LOOK

The west and central parts of the nation, like January will remain in a dry subsidence region with clearer skies and sunny weather. So that pattern we saw in January is likely to be repeated through the remainder of Summer and into March.


Issues now remain


  1. How heavy does the rainfall get on the east coast in association with the upper trough moving east and where does that fall? The risk is broad and the danger is widespread for the coming days for a return of significant flooding risks.

  2. The monsoonal flow developing north of the nation with a trough nearby, do we see tropical lows form in the early period as per the GFS or latter term as per the CMC and Euro and where do they go? That impacts rainfall.

These questions will be answered with very little lead time so if you are living in these regions be weather aware and pay attention to the forecasts as things will evolve quickly and sadly as with weather, people refer to social media NOWCASTING which offers you no lead time other than watching it unfold.


Lets take a look at when the pattern flips so that rainfall also comes back to WA and SA.


REMINDER

Riverine Flood Risk - This Week

The wet signal continues for the east of the nation and that is now going to lead to above average falls for many of you. Now it is a focus of where the heaviest of rainfall develops throughout the coming 1-2 weeks. The persistent SAM means that we are at the mercy of the constant easterly winds, feeding an inland upper trough and that will generate showers and thunderstorms. Moderate to heavy falls with daily thunderstorm activity will stack up over the course of 1-2 weeks. That may lead to inland areas seeing 100-200mm of rainfall through this period, not just coastal areas. The highest risk is over inland NSW and QLD and obviously the east coast from Gippsland in Victoria through to Thursday Island. Over the NT the risk is determined by the development and movement of the tropical lows north of the nation. That is the case for WA, where I have drawn in a low risk for now. This may change depending on any tropical system developing north of WA and turning towards the coastline through this period. The risk on land reflects the risk of cyclone activity impacting the nation, it somewhat goes hand in hand this time of year. But for now the major concern for me is over in the east.

SHORT TERM

The short term data is largely unchanged which is fine but it will not pick up on the heavier rainfall associated with thunderstorms so understand your number will vary in relation to thunderstorm activity over the east and north. Drier bias continues for the west for a good chunk of this period. Tropical rainfall likely to increase as we go through this week as the monsoon trough establishes and low pressure systems within the trough begin to deepen and head towards the northern regions bringing up enhanced rainfall chances.


UKMET - Rainfall Next 7 Days - MODERATE CHANCE

Note the heavy rainfall popping up on the east coast, that will be the area of significant concern moving over the coming days, I have issued charts and detailed analysis around the impacts of the potential heavy rainfall and flood risks. Flood charts have been issued for weeks in advance of this event.

ICON - Rainfall Next 8 Days - MODERATE CHANCE

Not as amplified as the UKMet.

MEDIUM TERM

The signal for rainfall remains high for the east coast and northern tropics with the MJO and positive SAM in place for the period, but some chance that we see both drivers begin to ease over the course of the first week of March. However that is not set in stone, it is an expectation given the 2 week wet phase and this being a natural response to the wet weather. That flip in the pattern may assist in bringing the rainfall chances back to WA and SA with tropical moisture being drawn south into troughs passing through southern Australia from west to east. The moisture will likely be ingested into the jet stream and dragged across the country IF this occurs.


CMC - Rainfall Next 10 Days - LOW CHANCE.

Some moderation in the rainfall signal on the CMC and GFS tonight but this is the ebb and flow of the modelling as it responds to the complex pattern.

EURO - Rainfall Next 10 Days

The Euro finally printing out what I have been suggesting with intense rainfall observed today being replicated in the coming days along the east coast. Severe storms inland over VIC, ACT, NSW and QLD to continue into next week. Monsoonal flow flirting with the north, just not quite making it onto the landmass but it is very close. West and central areas mostly dry for now, though southern WA could see storms increase this weekend.

ACCESS - Rainfall Next 10 Days - LOW CHANCE

Like the Euro last night, ACCESS suggests that after the heavy rainfall over the east coast with this first trough, a tropical system should drift down from the north and embed itself in the easterly flow bringing another burst of heavier rainfall next week. Showers and storms for the eastern inland, dry for the rest with maybe some light rainfall for inland WA and moderate falls near the coast with a middle level trough. Tropics not as amplified for the NT and WA.

KMA - Rainfall Next 12 Days - MODERATE CHANCE

The KMA also like the ACCESS suggesting what the Euro model was showing last night and drenching the east coast with a follow up tropical system doing a tour of duty along the east coast from N QLD through to about Newcastle. Rainy inland with a persistent trough for the coming 10 days before a colder drier airmass sweeps it out. Tropics not as amplified.

GFS - Rainfall Next 16 Days

Low chance with the model shifting run to run with very little confidence or consistency.

ENSEMBLE DATA

Good agreement in the spread and once again, you will not see the models pick up on the enhanced rainfall associated with thunderstorms, there is no model or data set that can tell you that, but the broader data sets suggest wet weather to peak over eastern and northern areas of the nation with the climate drivers. The wet weather may begin to spread out across the nation from the second week of March.


GFS - Rainfall Next 16 Days (median of 35 members) - MODERATE CHANCE.

Heavy rainfall over the northern tropics with the monsoonal flow and heavier rainfall over the east coast with heavy onshore winds. This is more likely, and if you check the deterministic above, the rainfall is likely to be more widespread.

CMC - Rainfall Next 15 Days (median of 30 members) - MODERATE CHANCE

Very wet for the east and north, that would equate to 1-2 months worth of rainfall in these regions, especially QLD and NSW. The pattern is complex and low confidence beyond about 5 days.

EURO - Rainfall Next 15 Days (median of 51 members) - HIGH CHANCE

Note the numbers coming up over the SE QLD and NE of NSW region hence the reason why I have ramped up the immediate flood threats. There will be follow up to that rainfall along the east coast. Moisture not as deep over the northwest in this run.

LONG TERM

As covered off in the longer term outlook, the weather is looking very damp as we move through March and possibly returning towards the end of the period into early April.


CFS - Rainfall Next 6 Weeks - MODERATE CHANCE

Continuing with the wet signal, probably more bias in the March period rather than April.

More severe weather coverage coming up tomorrow and a look at the broader weather picture including a La Nina review for Autumn and the impacts plus much more.