AXAU01 APRF 301914
IDW27600
TROPICAL CYCLONE TECHNICAL BULLETIN: AUSTRALIA - WESTERN REGION
Issued by AUSTRALIAN BUREAU OF METEOROLOGY TROPICAL CYCLONE WARNING CENTRE
at: 1914 UTC 30/03/2023
Name: Severe Tropical Cyclone Herman
Identifier: 21U
Data At: 1800 UTC
Latitude: 16.3S
Longitude: 105.8E
Location Accuracy: within 15nm (30 km)
Movement Towards: south southeast (151 deg)
Speed of Movement: 8 knots (15 km/h)
Maximum 10-Minute Wind: 95 knots (175 km/h)
Maximum 3-Second Wind Gust: 135 knots (250 km/h)
Central Pressure: 950 hPa
Radius of 34-knot winds NE quadrant: 60 nm (110 km)
Radius of 34-knot winds SE quadrant: 70 nm (130 km)
Radius of 34-knot winds SW quadrant: 70 nm (130 km)
Radius of 34-knot winds NW quadrant: 60 nm (110 km)
Radius of 48-knot winds NE quadrant: 35 nm (65 km)
Radius of 48-knot winds SE quadrant: 35 nm (65 km)
Radius of 48-knot winds SW quadrant: 35 nm (65 km)
Radius of 48-knot winds NW quadrant: 35 nm (65 km)
Radius of 64-knot winds:  nm ( km)
Radius of Maximum Winds: 10 nm (20 km)
Dvorak Intensity Code: T5.5/5.5/D2.5/24HRS STT:D1.0/06HRS
Pressure of outermost isobar: 1004 hPa
Radius of outermost closed isobar: 120 nm (220 km)
FORECAST DATA
Date/Time    : Location    : Loc. Accuracy: Max Wind   : Central Pressure
(UTC)        : degrees     :      nm  (km): knots(km/h): hPa
+06:  31/0000: 16.7S 106.2E:     030 (060):  090  (165):  955
+12:  31/0600: 16.9S 106.5E:     045 (080):  080  (150):  963
+18:  31/1200: 17.2S 106.9E:     050 (095):  070  (130):  972
+24:  31/1800: 17.4S 106.8E:     060 (115):  065  (120):  975
+36:  01/0600: 17.8S 106.6E:     085 (155):  045  (085):  989
+48:  01/1800: 17.9S 105.9E:     105 (200):  030  (055):  998
+60:  02/0600: 18.0S 104.8E:     135 (255):  030  (055):  999
+72:  02/1800: 17.8S 103.4E:     165 (305):  030  (055):  999
+96:  03/1800: 17.0S 100.4E:     195 (365):  030  (055):  999
+120: 04/1800: 15.8S  97.8E:     225 (420):  020  (035): 1001
REMARKS:
Severe Tropical Cyclone Herman has rapidly intensified overnight.  

The system was located using EIR imagery. With a well-defined eye, there is
high confidence in the position. Over the past 4 hours, eye patterns have been
yielding DTs in the range of 6.0-6.5. MET/PAT is 6.0 based on a strong D trend.
FT/CI are constrained to 5.5 (change of 1.0 over 6 hours/2.5 over 24 hours).  

Objective guidance (all 1-minute mean): SATCON 82kt at 1138Z, CIMSS ADT 95kt at
1800Z, NESDIS ADT 97kt at 1740Z, AiDT 97kt at 1800Z, CIMMS DMN 82kt at 12Z,
CIMMS OPEN-AIR 97kt at 18Z.  

Intensity set at 95 knots (10-minute mean) based on Dvorak analysis and
objective guidance.  

Deterministic and ensemble model guidance is consistent in significantly
underestimating the strength of the system. This may have ramifications for the
forecast motion and intensity changes of the system. 

Dry air wrapping around the north of Herman is yet to impact the core of the
system. An upper trough located to the south is providing good upper divergence
and a good outflow channel to the south. It is expected that TC Herman will
start to weaken when the dry air wrapping around the north (and possibly east)
of the system is ingested into the centre by moderate mid-level northerly winds
on the eastern periphery of the centre. The forecast is for this to occur by
later today, however there remains uncertainty given the poor performance of
model guidance up to this point. 

Herman is currently being steered to the southeast by the mid-level trough
located to the south of the system. When the system does start to weaken, the
upper levels should become separated and move to the south. Once this happens,
guidance suggests Herman will move steadily to the west under the influence of
the 700 hPa ridge. This should most likely occur on Saturday. If weakening is
delayed, southerly to southeasterly motion may occur for longer, but Herman is
still highly likely to remain well west of the Australian mainland. 

Copyright Commonwealth of Australia
==
The next bulletin for this system will be issued by: 31/0130 UTC.