Relocated - Maybe Cat1 at Landfall
Posted by JAC on 12/14/2009, 7:06 am



TROPICAL CYCLONE (TC) 06S (LAURENCE), LOCATED APPROXIMATELY 185 NM
WEST-SOUTHWEST OF DARWIN, AUSTRALIA, HAS TRACKED WEST-SOUTHWESTWARD
AT 05 KNOTS OVER THE PAST 06 HOURS. THE SYSTEM WAS RELOCATED FROM  
THE PREVIOUS 13/18Z WARNING POSITION OF 12.1S 126.9E TO THE CURRENT
POSITION BASED ON RADAR IMAGERY FROM WYNDHAM SHOWING A CONSOLIDATING
AND WELL-DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC). RE-ANALYSIS
INDICATES THAT THE LLCC BECAME QUASI-STATIONARY AFTER 13/06Z AND
TRACKED SOUTHWARD, STRENGTHENED, AND THEN TURNED WESTWARD OVER THE
PAST 06 HOURS. DUE TO THE LACK OF DATA E.G., QUIKSCAT AND VISIBLE
IMAGERY, THIS ERRATIC TRACK WAS NOT IDENTIFIED UNTIL RADAR IMAGERY
REVEALED THE STRONGER, TIGHTLY-WRAPPED LLCC. THE FORECAST TRACK AND
PHILOSOPHY HAVE ALSO BEEN CHANGED SIGNIFICANTLY DUE TO THE
RELOCATION. CURRENTLY, ANIMATED MULTISPECTRAL IMAGERY AND RADAR
DEPICT TIGHTLY-CURVED BANDING WRAPPING INTO THE CENTER. ANIMATED
WATER VAPOR IMAGERY INDICATES GOOD EQUATORWARD AND POLEWARD OUTFLOW.
TC 06S IS CURRENTLY TRACKING WEST-SOUTHWESTWARD UNDER THE STEERING
INFLUENCE OF THE LOW- TO MID-LEVEL SUBTROPICAL RIDGE OVER AUSTRALIA.
MODEL GUIDANCE SUPPORTS THE FORECAST WITH FAIR AGREEMENT BETWEEN THE
MODELS (GFDN, WBAR, TC-LAPS, NOGAPS, UKMO AND ECMWF). THIS FORECAST
IS BASED ON THE CONSENSUS AND TRACKS THE SYSTEM OVERLAND NEAR TAU
12, GRADUALLY WEAKENING THE SYSTEM AS IT PARALLELS THE COAST WITH
DISSIPATION EXPECTED BY TAU 48. IT IS POSSIBLE THE SYSTEM MAY TRACK
FURTHER NORTH ALONG THE COAST WITH LESS LAND INTERACTION AND
INTENSIFY AS HIGH AS 55-65 KNOTS IN THE NEXT 24 HOURS. MAXIMUM
SIGNIFICANT WAVE HEIGHT AT 140600Z IS 12 FEET.





FORECAST DATA
Date/Time   : Location    : Loc. Accuracy: Max Wind   : Central Pressure
[UTC]       : degrees     :      nm  [km]: knots[km/h]: hPa
+12: 14/1800: 13.2S 126.6E:     050 [095]:  045  [085]:  992
+24: 15/0600: 13.6S 125.6E:     080 [150]:  050  [095]:  989
+36: 15/1800: 14.1S 125.0E:     110 [210]:  050  [095]:  988
+48: 16/0600: 15.0S 124.8E:     145 [270]:  050  [095]:  989
+60: 16/1800: 15.9S 125.0E:     190 [355]:  045  [085]:  992
+72: 17/0600: 16.6S 125.0E:     240 [445]:  040  [075]:  995
REMARKS:
Latest fix for Tropical Cyclone Laurence is good, based on well-defined radar
and partially exposed LLCC on visible MTSAT imagery. Recent movement is west at
6 knots. Curved band pattern with 0.6 wrap gives DT=3.0. MET, PT and FT in
agreement.

Forecast track based on consensus of available 12UTC model runs biased with two
most recent ECMWF runs.  Track modified to match recent westward movement.
Resumption of westerly movement can be explained by building mid-level ridge to
the south. 500hPa steering pattern dominated by a ridge to the SE, so SW turn
expected.

Mid-level dry air in western sectors and weak vertical wind shear between low
and mid-levels expected to inhibit development rate for the first 24 hours, but
category 2 intensity could be reached before significant land interaction
occurs. Laurence, on its current forecast track, is expected to travel parallel
to the WA coast then turn southwards after around 48 hours under the influence
of a large upper trough moving in from the west. If the cyclone remains offshore
it may intensify further before increasing wind shear limits development.



Copyright Commonwealth of Australia
==

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Cyclone season has not... - hanna, 12/12/2009, 1:00 pm
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