Small RI
Posted by JAC on 12/15/2009, 11:54 am








REMARKS:
150900Z POSITION NEAR 14.6S 125.4E.
TROPICAL CYCLONE (TC) 06S (LAURENCE), LOCATED APPROXIMATELY 530 NM
NORTHEAST OF PORT HEDLAND, AUSTRALIA, HAS TRACKED SOUTHWESTWARD  
AT 06 KNOTS OVER THE PAST SIX HOURS. DESPITE ITS PROXIMITY TO THE
COAST, LAURENCE HAS INTENSIFIED TO NEAR 75 KNOTS (BASED ON 4.5
DVORAK FROM PGTW). OBSERVATIONS FROM TROUGHTON ISLAND INDICATE
SUSTAINED WINDS AS HIGH AS 74 KNOTS AS THE CYCLONE PASSED
APPROXIMATELY 12 HOURS AGO. IN CONTRAST TO THE PREVIOUS FORECAST,
THE SYSTEM IS NOW EXPECTED TO TRACK DEEPER INTO INTERIOR AUSTRALIA
AND DISSIPATE NEAR TAU 48 OVER LAND. AN UPPER LEVEL LONGWAVE TROUGH
POSITIONED ALONG 105E, AND EXTENDING AS FAR EQUATORWARD AS 10S, IS
EXPECTED TO AMPLIFY THE STEERING RIDGE TO THE EAST OF THE CYCLONE AS
IT APPROACHES. THIS WILL INHIBIT WESTWARD MOTION AS THE STEERING
FLOW STRENGTHENS OUT OF THE NORTH, DRIVING LAURENCE INLAND. ALL
AVAILABLE CONSENSUS MEMBERS, WITH THE EXCEPTION OF EGRR, INDICATE A
NOTICEABLE SOUTHWARD TURN INLAND BETWEEN TAU 24 AND 36, WITH MOST OF
THESE MEMBERS KEEPING THE CIRCULATION OVER LAND FOR 24 HOURS OR
GREATER. GFS, ECMWF, AND GFDN ATTEMPT TO PULL THE CIRCULATION BACK
OVER WATER, JUST NORTH OF PORT HEDLAND, AND SLOWLY REINTENSIFY THE
SYSTEM. IF THE CURRENT FORECAST TRACK VERIFIES, THEN THIS IS NOT
LIKELY TO OCCUR GIVEN THE DURATION THE CIRCULATION WILL BE OVER
LAND. HOWEVER, IF THE TROUGH FILLS PRIOR TO PASSAGE, THE CYCLONE
COULD CONTINUE TO TRACK ALONG THE COAST, MUCH STRONGER THAN
FORECAST, AND PROCEED BACK OVER WATER INTACT AND POSITIONED TO
REINTENSIFY. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 150600Z IS 16 FEET.
NEXT WARNINGS AT 152100Z AND 160900Z.


REMARKS:
Laurence is a small but intense system, as demonstrated by the observations at
Troughton Island earlier today, where a peak gust of 185 km/h was measured as
the system went directly over the island. An eye has been evident on IR,  VIS
and microwave imagery during the day. DT peaked at 6.0 but other images produced
a DT of 5.0-5.5. While DT may suggest 5.5 based on surround Black [no eye
adjustment LG/W], the FT is set at 5.0 in agreement with the PAT. ADT and AMSU
estimates are lower, probably owing to the small little on the weak side having
failed to identify the eye signature.

Laurence has intensified under favourable upper level outflow and low shear but
despite being in close proximity to land. Intensity is maintained at 85 knot
mean winds for next 18 hours as it tracks parallel to the coast, but intensity
is heavily dependent upon the influence of land. Most models suggest landfall is
the most likely scenario by about +24 hours and weakening is then likely as a
more southerly track ensues.  

A more westerly track is possible beyond +48 hours and potentially the system
may move offshore and redevelop in the longer term.

Copyright Commonwealth of Australia
==



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Laurence Dumping the NW Aussie Coast - JAC, 12/15/2009, 5:30 am
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