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TROPICAL CYCLONE TECHNICAL BULLETIN: AUSTRALIA – NORTHERN REGION

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TROPICAL CYCLONE TECHNICAL BULLETIN: AUSTRALIA – NORTHERN REGION

admin March 24, 2018
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TROPICAL CYCLONE TECHNICAL BULLETIN: AUSTRALIA - NORTHERN REGION
Issued by DARWIN TROPICAL CYCLONE WARNING CENTRE
at: 1944 UTC 23/03/2018
Name: Severe Tropical Cyclone Nora
Identifier: 22U
Data At: 1800 UTC
Latitude: 12.1S
Longitude: 139.4E
Location Accuracy: within 10 nm [20 km]
Movement Towards: southeast [141 deg]
Speed of Movement: 11 knots [20 km/h]
Maximum 10-Minute Wind: 85 knots [155 km/h]
Maximum 3-Second Wind Gust: 120 knots [220 km/h]
Central Pressure: 959 hPa
Radius of 34-knot winds NE quadrant: 90 nm [165 km]
Radius of 34-knot winds SE quadrant: 110 nm [205 km]
Radius of 34-knot winds SW quadrant: 90 nm [165 km]
Radius of 34-knot winds NW quadrant: 90 nm [165 km]
Radius of 48-knot winds NE quadrant: 45 nm [85 km]
Radius of 48-knot winds SE quadrant: 45 nm [85 km]
Radius of 48-knot winds SW quadrant: 45 nm [85 km]
Radius of 48-knot winds NW quadrant: 45 nm [85 km]
Radius of 64-knot winds: 25 nm [45 km]
Radius of Maximum Winds: 20 nm [35 km]
Dvorak Intensity Code: T5.0/5.0/D2.0/24HRS STT:S0.0/06HRS
Pressure of outermost isobar: 1002 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:  24/0000: 12.9S 140.0E:     020 [040]:  090  [165]:  957
+12:  24/0600: 13.7S 140.5E:     035 [065]:  090  [165]:  952
+18:  24/1200: 14.5S 140.8E:     045 [085]:  095  [175]:  946
+24:  24/1800: 15.2S 140.9E:     060 [110]:  100  [185]:  942
+36:  25/0600: 16.2S 141.0E:     080 [145]:  105  [195]:  936
+48:  25/1800: 16.6S 141.0E:     100 [180]:  105  [195]:  934
+60:  26/0600: 16.9S 140.8E:     120 [220]:  105  [195]:  935
+72:  26/1800: 17.1S 140.6E:     135 [255]:  100  [185]:  940
+96:  27/1800: 17.5S 138.4E:     180 [335]:  070  [130]:  970
+120: 28/1800: 18.6S 132.2E:     270 [500]:  030  [055]: 1001
REMARKS:
Recent satellite imagery depicts a well-structured, organised system, although
the ragged elongated eye briefly disappeared around 231700 UTC.

Confidence in the location of the LLCC is good, due to an eye on satellite
imagery, microwave and RADAR imagery. Recent movement has been towards the
southeast. 

Dvorak analysis DT numbers over the last 3 hours have ranged from 4.0 to 6.0
using an Eye Pattern and Curved band. Analysis at 1800 UTC based on a LG
surround. No positive eye adjustment was made, yielding a DT of 5.0.  Strong
development over the last 24 hours gave a MET of 4.5 and a PT of 5.0.  FT was
kept at 5.0.

A mid-level ridge building in the Coral Sea will continue to steer the system to
the southeast, before turning more southerly later today. A mid-latitude
mid-level trough amplifies as it passes to the south on Monday and Tuesday,
stalling the system, most likely in the southeastern Gulf of Carpentaria.  The
trough moves east during Tuesday, allowing a ridge to develop over eastern
Australia, pushing the system to the west.

Over the last 24 hours, the system has been located at the intersection of an
upper trough and ridge, providing good outflow both equatorward and poleward,
resulting in its rapid intensification. The upper ridge axis has now refocused
more to the north of the system, while the upper trough is weakening and
retrogressing westwards, increasing the northerly upper-level flow over the
system. CIMSS at 1800UTC indicated that the vertical wind shear over the system
has increased to northeasterly at around 20 knots. CIMMS analysis also indicates
that the equatorward outflow channel has already started to weaken, but
excellent outflow potential persists on the poleward side of the system. With
the upper trough weakening further over the weekend, this upper divergence will
continue to decrease over the next few days. The upper ridge axis reorganises
over the Coral Sea on Sunday, so the shear becomes briefly more favourable.

The decreasingly favourable upper pattern and shear over the next 24 hours
suggests that further rapid intensification is unlikely, and the system is
expected to develop at a standard rate, reaching peak intensity as a Category 4
[105 kn] tropical cyclone today or tonight. Environmental conditions on Sunday
remain marginally favourable, although some dry air entrainment may begin.
Maximum intensity of high-end Cat 4 is expected to be maintained, although the
possibility of further, slower development to Category 5 cannot be ruled out.
Increasing vertical wind shear, possible interaction with land and possible dry
air influence should restrict further development, and may slowly weaken the
system even if it remains over water on Monday and Tuesday. There is unlikely to
be any significant weakening ,however, until the system moves over land.

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