AXAU01 APRF 310720 IDW27600 TROPICAL CYCLONE TECHNICAL BULLETIN: AUSTRALIA - WESTERN REGION Issued by AUSTRALIAN BUREAU OF METEOROLOGY TROPICAL CYCLONE WARNING CENTRE at: 0720 UTC 31/03/2023 Name: Severe Tropical Cyclone Herman Identifier: 21U Data At: 0600 UTC Latitude: 17.3S Longitude: 106.5E Location Accuracy: within 15nm (30 km) Movement Towards: south southeast (150 deg) Speed of Movement: 6 knots (11 km/h) Maximum 10-Minute Wind: 110 knots (205 km/h) Maximum 3-Second Wind Gust: 155 knots (285 km/h) Central Pressure: 935 hPa Radius of 34-knot winds NE quadrant: 35 nm (65 km) Radius of 34-knot winds SE quadrant: 45 nm (85 km) Radius of 34-knot winds SW quadrant: 55 nm (100 km) Radius of 34-knot winds NW quadrant: 40 nm (75 km) Radius of 48-knot winds NE quadrant: 30 nm (55 km) Radius of 48-knot winds SE quadrant: 30 nm (55 km) Radius of 48-knot winds SW quadrant: 30 nm (55 km) Radius of 48-knot winds NW quadrant: 30 nm (55 km) Radius of 64-knot winds: 20 nm (35 km) Radius of Maximum Winds: 10 nm (20 km) Dvorak Intensity Code: T6.0/6.0/D2.0/24HRS STT:S0.0/06HRS Pressure of outermost isobar: 1006 hPa Radius of outermost closed isobar: 180 nm (335 km) FORECAST DATA Date/Time : Location : Loc. Accuracy: Max Wind : Central Pressure (UTC) : degrees : nm (km): knots(km/h): hPa +06: 31/1200: 17.4S 106.7E: 035 (060): 100 (185): 945 +12: 31/1800: 17.6S 106.8E: 045 (085): 085 (155): 959 +18: 01/0000: 17.9S 106.8E: 055 (100): 075 (140): 969 +24: 01/0600: 18.1S 106.8E: 065 (125): 060 (110): 978 +36: 01/1800: 18.4S 106.1E: 085 (155): 045 (085): 991 +48: 02/0600: 18.5S 105.2E: 110 (200): 030 (055): 1001 +60: 02/1800: 18.3S 104.1E: 130 (245): 030 (055): 1002 +72: 03/0600: 18.0S 102.9E: 160 (295): 030 (055): 1002 +96: 04/0600: 17.1S 100.6E: 210 (390): 025 (045): 1003 +120: 05/0600: 15.5S 97.4E: 255 (470): 020 (035): 1006 REMARKS: Slight intensification with Severe Tropical Cyclone Herman now a category 5 system. SAR microwave pass at 22:38 UTC suggested a maximum 1-minute mean wind of 143 knots, and along with increases in objective guidance contributed to reanalysis of 0000 UTC intensity to 110 knots (10 minute mean, category 5). The system was located using Visible imagery. With a well-defined eye, there is high confidence in the position. DT of 6.0 is analysed using an eye pattern, with OW eye, B surround and adjustment of 0.5. MET and PAT of 6.0 based on a D+ trend. FT/CI are 6.0. Most recent objective guidance (all 1-minute mean): SATCON 119kt at 0628Z, CIMSS ADT 125kt at 0630Z, NESDIS ADT 122kt at 0610Z, AiDT 122kt at 0630Z, CIMMS OPEN-AIR 121kt at 0530Z. Intensity set at 110 knots (10-minute mean) based on Dvorak analysis and objective guidance. While recent deterministic and ensemble model guidance have increased in intensity they remain 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 is wrapping around the north of Herman, and it may be beginning to impact the core. An upper trough, located to the south is providing good upper divergence and a good outflow channel to the south. It is expected that Herman will start to weaken imminently as the dry air wrapping around the north of the system is ingested into the centre by moderate mid-level northerly winds on the eastern periphery of the centre. However, there remains some uncertainty given the poor performance of model guidance up to this point and weakening may be delayed to this evening. 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 are forecast to become become sheared 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 is most likely to 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: 31/1330 UTC.