Tasmania

Seasonal climate risk information for Tasmania

Volume 3 | Issue 3 | 27 March 2020

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It’s been a wetter month particularly in the eastern half of the state. This has made increases to stored soil moisture particularly in the Midlands.

Oceans to the north of Australia are still capable of providing more moisture. Most models predict these warmer waters to hang around for some time.

In the Central Pacific, things are primed with generally more cool water than warm, from which four models are getting sniffs of a possible La Nina. The Trade Winds are also blowing a bit stronger which would need to happen for a La Nina to form later this year. Cloud patterns have come back from being El Nino like, to normal and pressure patterns are also normal. History tells me anything could happen in the Central Pacific from now on.

The Indian Ocean is just warm all over, with no phenomena apparent. Three models predict a negative IOD could pop up in late winter, but it’s very early for them to be making predictions about that, given IOD predictability isn’t very good this far out. Their signals are probably coming from a patch of undersea warmer water off Indonesia – so we’ll be watching that over the coming months.

Rainfall trigger mechanisms have shown drier tendencies. The SAM has been weakly positive and while it’s erratic in autumn, a neutral or negative SAM would fill you with more frontal confidence.

Pressure patterns are now in a summer pattern, not ideal for autumn and are forcing fronts and lows further south, this may happen further if higher pressure keeps encroaching from the west.

Unlike other states with sniffs of wetter, Tasmania has little guidance away from neutral forecasts for the next three months. Anything could happen with rainfall and temperature.

Do you want to hear the latest science, insights and innovations happening in the climate and agriculture space?  Then the 2020 Climate Webinar series is where you will hear from the experts from Agriculture Victoria, BoM, CSIRO and other agencies.  The series will run during lunchtime or you also have the option to listen to recordings at a time that suits.  The next webinar is:

Seasonal climate outlooks for Victoria, South Australia, Tasmania and Southern New South Wales. Dale Grey, Seasonal Risk Agronomist, Agriculture Victoria

Date: 10 am or 12 pm Wednesday 15 or Friday 17 April all South Eastern States.

Dale will explain in greater detail (45 minutes instead of 4 minutes) what the climate drivers and indicators are up to and predictions for winter and spring.

visit: http://agriculture.vic.gov.au/agriculture/weather-and-climate/climate-webinars
email: heather.field@agriculture.vic.gov.au

Soil moisture

The BoM Australian Water Resources Assessment (AWRA) modelled soil moisture map shows plant available soil moisture (10-100cm). The whole state and particularly eastern half of Tasmania has increased in soil moisture, it is now rated as average or wetter, and much wetter than normal in the north-east.

We would like to plot some publicly available dryland soil moisture probe values on this map for comparison, please contact us if you have remote telemetry, an upper and lower limit and are interested.

Model distribution summary for the next three months

Model distribution summary for the next four to six months

Model consensus forecast for the next six months

Sea surface temperature anomalies

Oceans to our north and south of the Equator are warmer than normal by some 0-5-1.5^oC and are an enhanced moisture source. Current value of the Dipole Mode Index is -0.07^oC (as of 25 March) which is neutral, as is normal for this time of the year. Sea surface temperature (SST) anomalies along the Equatorial Pacific cooled and then rewarmed to be unchanged for the month, currently at neutral temperatures. NINO3 is at +0.47^oC and NINO3.4 is +0.63^oC (as of 26 March).

Equatorial pacific sub-sea temperature anomalies

The Pacific Ocean Equatorial sub-surface temperatures anomalies have lost some warmth in the western Pacific this month. The cooler anomaly underneath the western Pacific has cooled further. Trade wind activity along the Equator, effected by tropical weather will dictate where the Pacific undersea heads in coming months..

Southern oscillation index

The SOI remains in neutral territory, currently at -0.7 (as at 25 March). Pressure patterns around the Equator as measured by this index are normal. The SOI will be worth watching once the northern wet season is over, usually by late April.

Pacific ocean surface wind anomalies

In February there was some reversal of the easterly Trade Winds near PNG, but during March this disappeared. The trade winds have remained lightly stronger in the Central Pacific. If this continues, cooling of the surface would most likely occur.

World cloudiness anomalies

Cloud at the International Dateline (180^oW) junction with the Equator has been slowly returning from high (blue colour) to more normal values.  This has probably been because the weak reversed Trade Wind feed into the Dateline has stopped, which was leading to El Nino like cloud patterns. If the trade winds stay stronger, expect less cloud in this region. Cloud is still lower to our tropical north due to higher pressure, but moister air is in abundance. There has been more cloud over southern Australia.

Southern annular mode

The Southern Annular Mode (SAM) or Antarctic Oscillation (AAO) has been weakly positive through March. In winter, a positive SAM can drag fronts away from southern Australia but during autumn SAM can have a variable effect on our climate. The NOAA 14-day forecast predicts the SAM to stay at similar values for a week and return to normal.

Air pressure

In the past 30 days, the Sub Tropical Ridge of High Pressure (STR) has stayed at a summer position situated over Melbourne. This pattern can start to block triggers to rainfall. Now that we are in autumn, we hope to see a northward migration of the pressure ridge at some time. This would indicate greater chances of frontal systems coming through. A pressure ridge off South-West Western Australia has been slowly propagating its way eastwards. Tasmania was yet to be under the influence of this.

Air pressure anomalies

The Sub Tropical Ridge of High Pressure has remained lower over Tasmania, indicative of unstable weather. The high-pressure ridge off WA has been slowly progressing eastwards, this might eventually start impacting on Tasmania. The high pressure in the Tasman Sea has moved further eastwards. The pressure is slightly higher at Darwin and normal at Tahiti. The SOI is normal.

Modelled Climate and Ocean Predictions for Tasmania from March 2020 run models