Over flight and satellite observations collected from the 24th-28th October 2009 have been used to update oil, oil patches and wax positions within the AMSA OIL-MAP Oil Spill Trajectory Model (OSTM). The recent satellite observations indicated that the slick was patches of oil/wax lying east and southeast of Montara extending to the south as patches (refer to Fig. 25.5). The winds have remained favourable over recent days which has seen the edge of the slick move parallel to the coast north-eastward rather than towards to coast. Using these observations, the latest wind and ocean forecast data has been incorporated to provide "search areas for oil and wax" for midday (Darwin Time) on the 30th and 31st of October 2009, as shown in Figs. 25.6 and 25.7 below. Please note that the brown dots in the figures
Fig. 25.5 AQUA Satellite Observation at UTC0500 28th October 2009. The darker colour within the red circle is indicative of surface oil slick; the white colour within the yellow circle indicates cloud
below indicate "search areas for oil and sheen". The density of the brown dots in the figure below indicates the likelihood of finding oil or wax in the various locations around the Montara well site. Due to the containment and dispersant operations, far field predictions are typically for defining search areas for scattered weathered oil and wax patches which may no longer be visible on the water's surface, hence this forecast is potentially a 'worst-case' depiction of the spill at this time.
The wind conditions for Montara are expected to be north-westerly winds (4-12 kts) for 30th October 2009, weakening from the north for 31st October, 2009. At the Montara well site, tidal oscillations are expected to be weak as we move through the neap tidal phase in the Timor Sea. The slick will generally drift southward over the forecast period. Fresh oil flows at Montara are predicted to be as follows:
• 30th Oct 2009: Weak SSE flow at 9 am; Weak SSW flow at 3 pm (4-12 knot NW winds);
• 31st Oct 2009: Weak SSW flow at 9 am; Weak NW flow at 3 pm (weak northerly winds);
To the far north in deep waters (The Timor Trench), the Indonesian Thru Flow current continues to flow strongly WSW. This strong flow is now spinning anticlockwise current eddies along the northern shelf-break which are moving position, allowing deepwater flows to spill over the shelf and drive the slick around Montara generally southward over the forecast period.
At Ashmore, Hibernia and Cartier Reefs, the forecast indicates that previously reported small patches of weathered wax will remain in the vicinity of Ashmore and Cartier Reefs. These patches were reported with dimensions of 50 x 50 m or less.
For waters between the West Atlas rig and the Kimberly coastline, the forecast indicates that the oil patches should drift slowly southward. The southeastern most position of this part of the slick (last described as very scattered small patches of wax) will remain north of Holithuria Banks. These patches may no longer be visible on the water's surface, and are not expected to reach any shorelines during the forecast period (APASA forecast bulletin 2009).
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