Latest detailed observed forecast and environmental conditions

Over summer, we monitor the health of the Great Barrier Reef to see how it's faring, as this time brings an increased risk of extreme weather, particularly heat waves, cyclones and flooding.

A detailed overview of the environmental conditions on the Reef is available below, and an overview of current conditions is also available.

Updates on current conditions are provided as part of our Reef Health Incident Response System.

Update 3: End of summer wrap up 2017/2018

Environmental condition

Summary of observations

Summary of past forecast from the Australian Bureau of Meteorology

Sea surface temperature (°C)

Throughout summer and into March and April, sea surface temperatures throughout the Marine Park fluctuated between average and above average. Some areas, particularly the inshore regions, experience periods of significantly above average temperatures. In March and April, small areas of the inshore Far Northern management area reached up to 4°C above average, whilst areas of Northern, and the inshore and mid-shelf regions of the Central and Southern reached up to 3°C above average.

Between 1 December 2017 and 31 March 2018, small patches of 80-100 Degree Heating Days (DHD’s) accrued in the Far Northern management area and the inshore Central and Southern management areas. 50-70 DHD’s accrued throughout the Far Northern and Southern management areas, as well as the inshore to mid-shelf regions of the Northern and Central management areas. The remainder of the Marine Park accrued 10 to 40 DHD’s.

Accumulated heat stress, in the form of degree heating days, is calculated by accumulating positive daily sea surface temperature anomalies.

This is relative to the appropriate long-term monthly mean, for 1 December to 31 March.

Degree heating day values can represent a broad range of thermal stress; e.g. three days at 1°C above the local long-term average results in the same degree heating day value as one day at 3°C (Bureau of Meteorology).

In December 2017, the Australian Bureau of Meteorology indicated:

  • the weak La NiƱa would be short-lived and dissipate in   autumn 2018
  • Queensland air temperatures between December and   February were likely to be warmer than average
  • sea surface   temperatures (based on the seasonal prediction system POAMA (Predictive Ocean   Atmosphere Model for Australia)) between January and March 2018 were likely to be average to slightly   above average in the northern half of the Marine Park, and average in the   southern half of the Marine Park

Tropical cyclones

No cyclones crossed the Great Barrier Reef coast this season.

Tropical Cyclone Iris initially formed in the Fiji region of the Coral Sea on 23 March 2018 prior to being downgraded to a tropical low after approximately 24 hours. On 29 March the system started to move in a WNW direction towards the north Queensland coast. The low re-strengthened to cyclone intensity (Category 1) on 2nd April.

Between 2nd and 5th April, Tropical Cyclone Iris tracked southeast, well offshore but parallel to the Queensland coast, from approximately Cairns to Mackay. During this time the system briefly intensified to a Category 2 (3rd April) and then downgraded back to a Category 1 (4th April) and a subsequently a tropical low (6th April). The system brought rain and damaging wind gales to the Central and Southern Great Barrier Reef, in particular the Mackay/Whitsundays region.

On 6th April the tropical low changed directions and began moving back towards the northwest. By 11th April, ex-TC Iris was in the northern Coral Sea.

As of 15/16th April, a very small low level circulation associated with ex-TC Iris remained in association with a trough which brought some short-lived heavy rainfall to the Cairns region.

  • The eastern region outlook indicated a near-average cyclone   season.
  • The average number of tropical cyclones in the eastern Australian   region is four each season, with at least one making landfall.

Rainfall levels

Between 1 October 2017 and 28 February 2018 (Northern wet season), rainfall levels in the Great Barrier Reef catchment were generally average to below average for the season. Exceptions include small areas of the Cape York region, and south east Queensland, which have received above average rainfall for the season.

During February, parts of the catchment received above average rainfall compared to the long-term monthly average.

Queensland had its 14th wettest March on record and its wettest March since 2012. Rainfall was well above average in the north and west of the State (Bureau of Meteorology).

  • The December to February seasonal outlook indicated   average rainfall was likely in the Great Barrier Reef catchment

Flood plumes

High rainfall resulted in numerous flood events affecting much of the northern tropics during this period, starting with major flooding on the northern tropical coast in the Herbert, Tully and Murray, Johnstone, and the Mulgrave and Russell catchments.

Towards the end of March, tropical cyclone Nora made landfall on the west coast of the Cape York Peninsula and renewed major flooding in the Herbert, Tully and Murray, and Mulgrave and Russell catchments, along with the Daintree and Barron catchments.

AIMS eReefs salinity at 1.5m depth (as of 27 March) indicated decreased salinity in parts of the Marine Park. This included inshore Far Northern (Princess Charlotte Bay), inshore to mid-shelf in the Northern (Wet Tropics regions) and inshore Central from approximately Tully south to Ayr. At the beginning of April pulses of freshwater continued into Princess Charlotte Bay, however as of mid-April these pulses had lessened, and salinity levels in the above mentioned areas were gradually returning closer to average salinity levels.

  • Major flood plumes usually follow above average rainfall conditions, driven   by monsoonal activity.
  • The seasonal stream-flow forecasts for December to February indicated   low flows were likely, with a chance of higher flows in north-eastern   Queensland