Tasmania - Fast Break

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You are reading the 6th Fast Break for Tasmania

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Volume 1 | Issue 6 | Tasmania | Published: 02 Oct 2018

Welcome to our sixth “Fast Break” newsletter for the Tasmanian grains industry. Our team has been preparing this monthly newsletter for 12 years in Victoria and with GRDC support we are now able to present it for Tasmania. If you like it, please consider passing it on through your networks and subscribing.

Still no sign of an El Niño and yet the majority of models predict one will occur in late spring/summer. The Pacific Ocean surface is still neutral, the SOI is vaguely interested, the cloud patterns aren’t remotely keen, the deep sea is warm to depth, but only in the western and central Pacific. The major change this month is the easterly trade winds have shown some El Niño like behaviour, with at least two, one-week long reversals of significant strength from PNG to half way across. This is likely to force the warmer water to depth further to the east, and warm the surface in the middle of the Pacific. All this is likely to take months which will just about see out the growing season before it occurs. Historically, summer El Niño’s have been hit and miss for Tasmania.

The Coral Sea is still warmer which is most unlike a “classic” El Niño.

All action has been in the Indian Ocean for some months. In the last weeks the Dipole Mode Index (DMI) measurement of the IOD has gone positive. Despite predictions from models for its occurrence all season, it has only just happened. We have had +IOD like cooling in the Timor Sea for many months but the current +IOD condition is being caused by the rapid warming off the African coast. Trade wind patterns are not consistent with a proper +IOD, but the lack of cloud off Sumatra is. Certainly, the lack of NW moisture feed for much of the season had something to do with the Indian Ocean not playing ball. If the +IOD hangs around for two months it will be called an event, but it would normally die in late October early November when the tropical wet season fires up. Historically around 50-60 of springs in +IOD years have been in the driest third of records.

Pressure patterns, which were favourable in August, have deteriorated in September by increasing in pressure and position over the SE mainland and chasing rainfall triggers further south of Tasmania. Such behaviour is classic +IOD induced.

The SAM which had been behaving itself in winter (particularly for the west of Tasmania) will cease to be a major driver in spring. Connections to tropical moisture will be more important than weak fronts.

The models surveyed are predicting drier/average conditions for spring with average/warmer temperatures.

It would be prudent to plan for the possibility of a shorter spring.

map of Tasmania showing adequate soil moisture to depth
The BoM AWRA modelled soil moisture map shows plant available soil moisture (10-100cm) has decreased through the Midlands during September. Values aren’t desperate (in the 12-40% range), but aren’t exciting either. The Freycinet hinterland remains dry. We would like to plot some publically available 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
Graphs showing the distribution of September-November modelled rainfall as average/drier and likely average temperature
graphs showing a consensus for December-February modelled rainfall as average with warmer temperatures.

Model consensus forecast for the next six months

Model consensus forecast for the next six months

Current outlook (28 September)

Previous outlook (27 August)

Oct-Dec outlook

Oct-Dec outlook

Jan-Mar outlook

Jan-Mar outlook

Pacific Ocean

El Niño (Modoki)

El Niño (Modoki)

El Niño

El Niño

Indian Ocean

Neutral

Neutral

Neutral (+IOD?)

Neutral

Rainfall

Average/slightly drier

Average

Average/slightly drier

Average

Temperature

Slightly warmer

Slightly warmer/average

Average

Warmer

Equatorial Pacific Ocean Sea surface temperature anomalies are normal. But a +IOD has formed in the Indian Ocean
Sea surface temperatures (SST) along the Equatorial Pacific cooled off a small amount in August. NINO3 is at +0.16oC and NINO3.4 is +0.29oC (as of 30 August), both at neutral values and nothing like El Niño. The Coral Sea is still a bit warmer, a good sign for our major moisture source. In the Indian Ocean the cool patch of water off Java has moved a little westward and has recently started to recede. Official values of the IOD are neutral but this pattern is still +IOD like near Indonesia but completely neutral off Africa. Warmer tropical ocean anomalies nearer to Australia can provide more evaporation as a moisture source, whereas cooler ocean anomalies can kill the moisture source.
Undersea warm temperatures in the eastern Pacific have cooled, nothing like El Niño.
The Pacific Ocean Equatorial sub surface temperatures actually cooled in the far east, not what you would expect if an El Niño was forming. The autumn attempt at El Niño has failed thus far. A large patch of warmer water in the central Pacific is moving eastward and may be a second attempt. For an El Niño to occur we would need to see trade winds reverse and the SOI to go strongly negative as well
The SOI value is currently at -6.7
The SOI is currently at -6.8 and stable (as of 28 August), negative, but close to neutral. Pressure patterns around the Equator as measured at Darwin and Tahiti are normal. Sustained values of the SOI greater or less than 8 are meaningful and can indicate El Niño (when negative) and La Niña (when positive).
The Equatorial Pacific trade winds have been mostly normal throughout September, but mid-month a short lived strong reversal happened near PNG
The Equatorial Pacific Easterly Trade Winds have been normal through August (shown by the small arrows). Mid-month the trade winds experienced a short sharp reversal for a week near PNG. Expect this to keep the warm water moving underneath to the east. Due to the wind reversal not getting to the central Pacific it’s unlikely the ocean surface will warm. Reversed trade winds are needed to kick off an El Niño and to maintain it.
Cloud is slightly less than normal at the junction of the Equator with the Dateline, but less cloud exists off Sumatra.
Cloud at the International Dateline (180oW) junction with the Equator has decreased (brown colour) in the last 30 days more suggestive of La Niña. The lack of cloud off Sumatra remains +IOD like, but the large lack of cloud off Africa is inconsistent with +IOD,
the SAM has spent August moderately negative
The Southern Annular Mode (SAM) has spent most of August in moderate negativity. This has allowed an increase in the proximity and frequency of fronts across Tasmania. The BoM and NOAA models suggest a move to moderate positivity of the SAM in coming weeks. SAM has its greatest influence over frontal system positioning to Tasmania during winter. Positive SAM pulls fronts away from southern Australia and negative SAM pushes them towards us.
the STR of high pressure has been in a higher than normal winter position at the top of the Bight
In the past 30 days, the Sub Tropical Ridge of High Pressure has remained at a higher than normal position allowing plenty of fronts across Tasmania. The predominately western wind flow leads to a rain shadow affect in the far east.
pressure at Darwin and Tahiti are both normal, while pressure over SE Australia has been lower
The Sub Tropical Ridge of High Pressure was lower in pressure over SE Australia meaning no impediment to fronts and lows. Often this means more rainfall in winter. Pressure at Darwin is normal and lower at Tahiti which is why the SOI is slightly negative. The higher pressure over the whole of the Tropical Indian Ocean is not helpful for getting moisture down to us.
12 climate models show their predictions for the next six months for the Pacific Ocean, Indian Ocean, rainfall and temperature for Tasmania.
Download this table in word format here

Modelled Climate and Ocean Predictions for Tasmania from August 2018 run models

Modelled Climate and Ocean Predictions for Tasmania from August 2018 run models

Ocean-Atmosphere Coupled Models

Multi Model Ensembles

Statistical

System 5

ECMWF

Europe

POAMA2

BoM

Australia

SINTEX-F

JAMSTEC

Japan

CFSv2

NCEP

USA

GEOS-S2S

NASA

USA

ENS

JMA

Japan

CSM1.1

BCC

China

UKMO

GloSea5

UK

NMME

USA

APCC

Korea

EUROSIP

Europe

SOI phase

USQ/Qld

Australia

Month of Run

August

August

August

August

August

August

August

August

August

August

August

August

Forecast months

SON

SON

SON

SON

SON

SON

SON

SON

SON

SON

SON

SON

Rainfall Skill

Low/Moderate

NA

NA

Moderate

Moderate

Moderate

NA

Moderate/

Low SW

Moderate

NA

NA

NA

Spring Pacific Ocean NINO3.4

Warm

(weak El Niño)

Neutral

Warm

(El Niño Modoki)

Warm

(El Niño)

Slightly warm

Warm (weak El Niño Modoki)

Warm

(El Niño

Modoki)

Warm

(El Niño Modoki)

Warm (El Niño Modoki)

Slightly warm

Warm (El Niño Modoki)

-

Spring Eastern

Indian Ocean

Cool (+IOD like)

Neutral

Cool (+IOD)

Neutral

Neutral

Neutral

Slightly cool

Slightly cool

(+IOD like)

Cool (+IOD)

Neutral

Neutral

-

Spring Rainfall

Average

Slightly drier N, average S

Average

Slightly drier

Average E, slightly drier W

Average

Average

Slightly drier

Slightly drier

Average

NA

Average E, slightly wetter W

Spring Temperature

Slightly warmer

Slightly warmer E, average W

Slightly cooler

Average N, slightly warmer S

Average

Average

Average

Average

Average

Average

NA

-

Forecast months

DJF

DJF

DJF

DJF

DJF

-

DJF

NDJ

DJF

DJF

NDJ

-

Summer Pacific Ocean NINO3.4

Warm

(El Niño)

Neutral

Warm

(El Niño Modoki)

Slightly warm

Warm

(weak El Niño)

-

Warm

(El Niño

Modoki)

Warm

(El Niño)

Warm

(El Niño)

Warm

(El Niño Modoki)

Warm (El Niño Modoki)

-

Summer Eastern

Indian Ocean

Neutral

Neutral

Neutral

Slightly warm

Slightly warm

-

Slightly cool

Neutral

Neutral

Neutral

Neutral

-

Summer Rainfall

Average

Slightly drier

Average

Average

Average

-

Average

Average

Average

Average

NA

-

Summer Temperature

Slightly warmer

Slightly warmer

Slightly cooler W, average E

Slightly warmer

Slightly warmer

-

Average

Average

Slightly warmer

Slightly warmer

NA

-

Notes

Operational

Operational

Experimental

Operational

Experimental

Experimental

Operational

Operational

Experimental

Summary of 4 dynamic models

Experimental

Summary of 8 dynamic models

Experimental

Summary of 5 dynamic models

5 phase system based on previous 2 months SOI