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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