SPAC: 30U - Post-Tropical

[Subtrop]

97P INVEST 250413 0600 11.5S 136.7E SHEM 20 1007

[cycloneye]

REMARKS:
Tropical Low 30U is slow moving near land in the eastern Gulf of Carpentaria.
Deep convection has weakened and become more disorganised in the last 3 hours.
Position is based on persistence, animated VIS satellite imagery and Weipa
radar with moderate confidence.

Dvorak analysis: FT/CI=2.0/2.5. DT 2.0 based on 0.35 wrap of log10 spiral.
24-hr trend of W- gives MET2.0 and PT is 2.0. Objective guidance at 0000 UTC:
ADT 33 kn, AiDT 28 kn, DPRINT 25 kn, DMIN 24 kn, MW Sounder 38 kn and SATCON 35
kn (all 1-min average). Intensity is set at 25 kn based on persistence from the
overnight ASCAT pass, with gales expected to develop on the southern side early
Sunday morning.

30U lies on the western edge of an upper anticyclone, under moderate
northeasterly shear (CIMSS 23 kn). MIMIC TPW indicates incursion of mid-level
dry air from the north and northeast, which is also present on 2300 UTC Weipa
trace. SST are around 30C. The moderate deep layer NE'ly shear is likely to be
maintained, and in the absence of any strong low level forcing, likelihood of
much further development would seem limited. General model guidance indicate a
balanced steady state during the weekend and into early next week with periods
of quadrant gales, possibly associated with pulsating deep convection near the
centre.

The system is expected to be slow moving through Saturday. A low to mid-level
anticyclone to the southeast is likely to become the dominant influence from
tonight, resulting in 30U turning towards the west and steering across the Gulf
of Carpentaria over the next few days. The track will take 30U close to the
northeast Top End coast on Monday, before 30U continues to move into the
Arafura Sea where it is likely to persist for most of next week.

[cycloneye]

REMARKS:
Tropical Low 30U has a moderate chance of developing into a tropical cyclone
overnight Sundaya and during Monday.

There has been an increase in convection to the south of the system during the
last 6 hours. Position is based on Weipa radar and an afternoon microwave pass
with only moderate confidence.

Dvorak analysis: DT = 2.5 based on a three hour averaged curved band pattern
with 0.3 to 0.4 wrap. MET is 3.0 based on a 24 hour D trend, with a PAT
adjustment down to 2.5. FT/CI 2.5. Prolonged proximity to land is likely to be
decreasing the skill of subjective Dvorak as an intensity estimator. Objective
guidance at 1140 UTC: ADT 41 kn, AiDT 36 kn, DPRINT 27 kn, DMINT 28 kn (0832
UTC), and SATCON 34 kn (0930 UTC) (all 1-min average). Intensity is maintained
at 30 kn.

Conditions are moderately favourable for development with a moist environment,
warm SSTs and analysed shear of about 10 knots from the NE. Despite this model
guidance suggests the system is not vertically stacked through the full depth
of the troposphere. A short wave trough is moving eastwards to the south of 30U
during Monday and Tuesday which may aid upper outflow and divergence. The
system has the best chance of developing into a tropical cyclone during Monday
as it moves westwards across the Gulf of Carpentaria and during this time it is
likely to have gales in southern quadrants. From Tuesday as it moves north of
the Top End conditions become less favourable.

A low to mid-level anticyclone is forecast to develop south of the system later
tonight and will cause 30U to turn towards the west, moving across the Gulf of
Carpentaria tonight and Monday. The track will take 30U close to the northeast
Top End coast during Monday, and gales may occur about land areas at that time.
On Tuesday 30U will continue to move into the Arafura Sea where it is likely to
persist for most of next week. The environment there is likely to be
unfavourable and the system has only a low chance of developing into a tropical
cyclone from Tuesday onwards.

[cycloneye]

REMARKS:
Tropical Low 30U is off the eastern Top End, just north of Nhulunbuy moving
northwest to the Arafura Sea. Convection near the centre has decreased during
the last 6 hours, with a limited amount of convection to the south of the
centre. Position based on animated visible satellite imagery, observations at
Gove Airport and Cape Wessel, and extrapolation of earlier scatterometry, with
fair confidence.

Dvorak analysis: DT = 1.5 based on a three hour averaged curved band pattern
with 0.2 to 0.3 wrap. MET is 1.5 based on a 24 hour W trend, with PAT also 1.5.
FT is 1.5 based on MET/PAT, and CI is held at 2.0 with initial weakening.
Objective guidance at 1100 UTC (1 minute means): ADT 47 kn, AiDT 37 kn, and
DPRINT 29 kn, and DMINT (0930 UTC) 28 kn. Intensity is decreased to 30 kn based
on easing of convection, and while the centre of 30U remains over water the
system is likely interacting with land. This is generally consistent with
guidance.

Environmental conditions are relatively balanced. CIMSS analysed shear remains
low at 12 kn northeasterly, SSTs are favourable along the track (28-29C), and
an upper trough to the south is enhancing poleward outflow. This is offset by
lack of low level forcing and bursts of dry continental air periodically
encroaching from the south. There is some chance that gales redevelop in
southern quadrant during the next 6 hours, though as the system continues to
interact with land and subsequently moves north into less favourable shear this
is becoming less likely.

A low to mid-level anticyclone is steering 30U to the northwest, close to the
northeast Top End coast. On Tuesday, 30U will continue to move northwest in the
Arafura Sea where it is likely to persist for most of next week. The
environment there is forecast to be less favourable with drier southerlies
pushing the system north under stronger easterly shear. However, there remains
a low risk of further development throughout the week.

[cycloneye]

REMARKS:
Tropical Low 30U is moving northwest in the Arafura Sea. Deep convection has
weakened, and no organisation of deep cloud is evident.

Position based on radar and animated satellite imagery with moderate
confidence.

Dvorak analysis: As the deep convection has weakened, there is no longer a
suitable Dvorak pattern to apply to the current satellite imagery. MET is 1.5
based on a 24 hour S trend, with no adjustment. FT is 1.5 based on MET with CI
held at 2.0 for initial weakening and for the potential convection
redevelopment that could occur with the diurnal maximum over the next 6 to 12
hours. Objective guidance at 1200 UTC (1 minute means): ADT 41 kn, AiDT 35 kn,
DPRINT 28 kn, D-MINT 24 kn (0947 UTC), SATCON 40 kn. Intensity is set at 30 kn
based on earlier scatterometry and a strong consensus of intensity guidance
indicating a 30-knot wind maxima in the southwest quadrant.

Environmental conditions are marginally favourable. SSTs are 28-29C along the
forecast track, there is ample atmospheric moisture and an upper trough to the
south enhancing poleward outflow. CIMSS analysed shear at 1200 UTC is 17 kn
from the east however, and is expected to increase further. With the lack of
organisation and deep convection currently observed it is unlikely there will
be sufficient opportunity for 30U to intensify into a tropical cyclone before
the increasing shear and decreasing Coriolis makes the environment unfavourable
for development.

A low to mid-level anticyclone is steering 30U to the northwest. Strengthening
upper-level easterlies on Thursday will cause 30U to become a shallower system
that then moves back towards the southeast on Friday under the influence of a
mid-level trough passing to the south.

An upper-level trough that passes to the south on the weekend may provide
another opportunity for 30U to strengthen as shear reduces again.