AXAU01 APRF 010134
IDW27600
TROPICAL CYCLONE TECHNICAL BULLETIN: AUSTRALIA - WESTERN REGION
Issued by AUSTRALIAN BUREAU OF METEOROLOGY TROPICAL CYCLONE WARNING CENTRE
at: 0134 UTC 01/04/2023
Name: Severe Tropical Cyclone Herman
Identifier: 21U
Data At: 0000 UTC
Latitude: 18.6S
Longitude: 107.1E
Location Accuracy: within 15nm (30 km)
Movement Towards: south southeast (162 deg)
Speed of Movement: 3 knots (6 km/h)
Maximum 10-Minute Wind: 105 knots (195 km/h)
Maximum 3-Second Wind Gust: 145 knots (270 km/h)
Central Pressure: 940 hPa
Radius of 34-knot winds NE quadrant: 30 nm (55 km)
Radius of 34-knot winds SE quadrant: 40 nm (75 km)
Radius of 34-knot winds SW quadrant: 50 nm (95 km)
Radius of 34-knot winds NW quadrant: 50 nm (95 km)
Radius of 48-knot winds NE quadrant: 25 nm (45 km)
Radius of 48-knot winds SE quadrant: 25 nm (45 km)
Radius of 48-knot winds SW quadrant: 25 nm (45 km)
Radius of 48-knot winds NW quadrant: 25 nm (45 km)
Radius of 64-knot winds: 15 nm (30 km)
Radius of Maximum Winds: 10 nm (15 km)
Dvorak Intensity Code: T5.5/6.0/W0.5/24HRS STT:D0.5/06HRS
Pressure of outermost isobar: 1008 hPa
Radius of outermost closed isobar: 150 nm (280 km)
FORECAST DATA
Date/Time    : Location    : Loc. Accuracy: Max Wind   : Central Pressure
(UTC)        : degrees     :      nm  (km): knots(km/h): hPa
+06:  01/0600: 19.1S 107.1E:     035 (065):  090  (165):  955
+12:  01/1200: 19.4S 107.2E:     045 (085):  070  (130):  972
+18:  01/1800: 19.6S 107.1E:     060 (110):  050  (095):  988
+24:  02/0000: 19.8S 106.8E:     070 (130):  045  (085):  992
+36:  02/1200: 20.0S 106.2E:     080 (150):  035  (065):  998
+48:  03/0000: 20.0S 105.4E:     110 (205):  030  (055): 1002
+60:  03/1200: 19.8S 104.7E:     140 (260):  030  (055): 1002
+72:  04/0000: 19.2S 103.5E:     175 (325):  030  (055): 1004
+96:  05/0000: 17.9S 100.7E:     225 (415):  030  (055): 1003
+120: 06/0000: 16.7S  98.2E:     285 (530):  025  (045): 1006
REMARKS:
Severe Tropical Cyclone Herman has weakened to a category 4 system.  

The eye continues to show weakening signs with fluctuating eye temperatures,
and the latest EIR imagery shows the surrounding cloud tops warming.   

Intensity: 105 kn based upon Dvorak holding CI=6.0 higher than FT=5.5 for
weakening. The eye pattern has been ranging between 5.5-6.0 DT with white
surround (6.0) and eye temperature adjustment ranging   0.5 to 0. Adjusted MET
on a weakening trend of 5.5. The analysis is consistent with objective ADT
FT/CI=6.0/6.6. Other objective guidance broadly consistent (all 1min mean):
SATCON 98kn; ADT 120kn; and AiDT=116kn.  

Structure: SMOS, and AMSR2 passes show gales extending only 30-50nm from
centre.  

Motion: Herman is currently being steered to the south southeast by the
combined influences of the ridge to the east and the mid-level trough but the
influence of the trough is expected to weaken as it slips further away.  

The environment is becoming more hostile to the circulation    shear has
slightly increased remains N at 15-20kn with ongoing poleward upper level
outflow associated with an upper trough away to the south southeast,  the
peripheral dry air may be impacting the circulation. SSTs are 27.5C.   

Herman is highly vulnerable to the dry air being ingested into the circulation
as it expected to wrap around from the north and hence weakening is expected to
be rapid during the weekend. 

Deterministic and ensemble global model guidance has been significantly
underestimating the strength of the system, not surprising given its small
size.  This has affected the track with some guidance taking it on a more
westerly track sooner than what is expected under the influence of a ridge to
the south.  

Nevertheless Herman is still highly likely to remain well west of the
Australian mainland and have no direct impact upon the coast. 

Copyright Commonwealth of Australia
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The next bulletin for this system will be issued by: 01/0730 UTC.