SPAC: 33U - Tropical Low

[Subtrop]

93P INVEST 250507 1800 8.9S 141.5E SHEM 15 1006

[Pasmorade]

B. TROPICAL DISTURBANCE SUMMARY:
(1) THE AREA OF CONVECTION (INVEST 93P) PREVIOUSLY LOCATED NEAR
9.0S 141.3E IS NOW LOCATED NEAR 7.7S 138.1E, APPROXIMATELY 285 NM NORTH-
NORTHEAST OF GOVE AIRPORT, NHULUNBUY, AUSTRALIA. ANIMATED MULTISPECTRAL
SATELLITE IMAGERY (MSI) DEPICTS A BROAD AND SLOWLY CONSOLIDATING
PARTIALLY-EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) WITH FLARING
CONVECTION. ENVIRONMENTAL ANALYSIS REVEALS A MODERATE TO UNFAVORABLE
ENVIRONMENT FOR DEVELOPMENT WITH MODERATE TO HIGH VERTICAL WIND SHEAR OF
20-25 KNOTS, GOOD POLEWARD UPPER-LEVEL OUTFLOW, AND WARM SEA SURFACE
TEMPERATURES (SST) OF 28-29C. DETERMINISTIC AND ENSEMBLE MODELS ARE IN
GOOD AGREEMENT THAT INVEST 93P WILL CONTINUE TO TRACK GENERALLY
WESTWARD, THEN REMAIN NEAR THE ARAFURA SEA AND SLOWLY DEVELOP OVER THE
NEXT 24-48 HOURS. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 20 TO
25 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1006 MB.
THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE
WITHIN THE NEXT 24 HOURS REMAINS MEDIUM.

06:00 UTC update

[cycloneye]

Less than 5% (Very Low) chance of tropical cyclone strength on Saturday 10 May at 10:00am AEST.

[Sciencerocks]

[cycloneye]

REMARKS:
Tropical low 33U is slowly consolidating near the coast of West Papua.

Position based on animated visible satellite imagery with moderate confidence
as the mid-level circulation is displaced to the southwest of the surface
circulation.

Dvorak DT of 2.0 based on curved band with a 0.3 wrap. MET is 1.5 based on D-
trend with PAT adjusted to 2.0. FT/CI 2.0. Intensity is 25 knots based on
earlier scat passes and in agreement with Dvorak. D-PRINT is 21 kts (1-min) and
is the only objective aid available for now.

33U is in a favourable environment for further development with ample
atmospheric moisture and low to moderate shear of approximately 10-15 knots. An
upper trough to the southwest is providing good upper divergence. As the trough
passes to the south the upper divergence is expected to improve during Saturday
night and continue into Sunday providing a good opportunity for 33U to develop
further. From Monday the same trough then begins to increase the shear over 33U
and it is expected to weaken again.

Due to its small size 33U could develop quickly, however it's low latitude and
proximity to land could limit the rate of intensification. Peak forecast winds
are currently 40 kts but with gales confined to the southern side, aided by the
sub-tropical ridge.

Over the next 24-48 hours motion is expected to be slow with low level easterly
winds on the southern side due to the low-level ridge to the south, balanced by
both some cross-equatorial westerly winds to the north and westerly winds in
the mid to upper levels due to the mid-upper trough on the southern side. If
33U strengthens and becomes a deeper system then the trough to the south
becomes more likely to steer 33U slowly further south. As the shear increases
on Monday, 33U will become a shallower system and move to the northwest due to
the persistent low level south easterly winds. While forecast models generally
agree with this scenario, there are a few that maintain a weaker tropical low
that moves over Papua and dissipates.

[Sciencerocks]

 https://x.com/hurricane_chase/status/1921367987367424023

[cycloneye]

REMARKS:
Tropical Low 33U remains near land to the southwest of Papua New Guinea. The
deep convective cloud structure has weakened slightly since this morning, with
less curvature evident, however the system maintains a robust low level
circulation on animated satellite imagery, and a new convective burst has
recently developed to the SW of the estimated low level centre. Position based
on animated visible satellite imagery and extrapolation of the 0155 UTC GMI
microwave pass, with good confidence.

Dvorak DT of 2.0 is based on a curved band pattern with 0.35 wrap. MET is 2.0
based on a 24-hour S trend with no PAT adjustment. Final T is 2.0, and CI is
held at 2.5. Intensity maintained at 35 knots extrapolating from the 00 UTC
ASCAT pass, consistent with subjective Dvorak. Gales continue to be analysed to
the southwest of the system only.

The environment remains favourable for development, with ample atmospheric
moisture, warm waters and an upper trough to the southwest assisting with
outflow to the south, while the centre of the system remains under low CIMSS
analysed deep layer shear. Of note, the analysed upper divergence has steadily
decreased since the 00 UTC analysis as the deep convection has waned. These
favourable conditions are offset by proximity to the land mass of Papua New
Guinea, which will be the main inhibitor to development over the next 12 to 18
hours. A steady state intensity is forecast in the short term with intermittent
gales persisting to the south of the centre. Beyond that, northerly wind shear
from an amplifying upper trough to the southwest will cause conditions to
become more unfavourable, and weakening is forecast from 00 UTC tomorrow.

Motion is expected to remain slow over the next 6-12 hours, with 33U situated
near the col between two weak mid-level ridges. As the shear increases on
Monday, there is broad consensus amongst forecast models that 33U will become a
shallower system and move to the northwest due to the persistent low level
south easterly trade flow.

[Sciencerocks]

[cycloneye]

REMARKS:
Tropical Low 33U has started to move towards the west northwest, and is located
near the island of Dolok. The deep convective cloud remains displaced to the
south of the low level centre, despite the current low deep layer shear.
Position based on extrapolated motion from a 1202 UTC ASCAT-B pass, with
moderate confidence.

Dvorak DT of 2.5 is based on a shear pattern with the centre around half a
degree from the edge of the deep convection. MET/PAT is 2.0 based on a 24-hour
S trend . FT is 2.0, with CI held at 2.5 during weakening. Intensity maintained
at 35 knots based on the 1202 UTC ASCAT pass, with gales analysed to the
southeast of the system only. Objective guidance (1-min mean and at 1800 UTC
unless otherwise stated): ADT 51 kts, AiDT 39 kts, DPRINT 32 kts, DMINT 33 kts
(1328 UTC), SATCON not available.

The environment is still favourable for development, with ample atmospheric
moisture, warm waters and an upper trough to the southwest assisting with
outflow to the south, while the centre of the system remains under low CIMSS
analysed deep layer shear. These favourable conditions are offset by proximity
to the island of Dolok, just off the coast of New Guinea, which will be the
main inhibitor to development over the next 12 hours. The analysed upper
divergence also remains displaced to the southeast of 33U. A steady state
intensity is forecast in the short term with intermittent gales persisting to
the south of the centre for another 6-12 hours. Beyond that, northerly wind
shear from an amplifying upper trough to the southwest will cause conditions to
become more unfavourable, and weakening is forecast after 00 UTC Monday.

Recent motion has been towards the west northwest. As the shear increases on
Monday, there is broad consensus amongst forecast models that 33U will become a
shallower system and move more rapidly to the west northwest due to the
persistent low level south easterly trade flow.

[cycloneye]

REMARKS:
Tropical Low 33U continues to weaken and has no chance of intensifying.
The low-level circulation remains poorly defined with ongoing deep convection
displaced southeast of the centre. Position in the Arufura Sea near the West
Papuan Island of Dolok is based on animated visible imagery with only moderate
confidence and likely elongated to a second centre to the southeast.
Intensity Vm=30kn located southeast of the centre based on a combination of
OSCAT 0311 UTC winds, model guidance and Dvorak.
Dvorak DT=1.5 is based on a shear pattern with the centre now over a degree
removed from the deep convection. MET = 1.5 based on a 24-hour D- trend and
FT/CI=1.5/2.0. Objective guidance (1-min mean at 0530 UTC unless otherwise
stated): ADT 34 kn, AiDT 33 kn, DPRINT 29 kn, DMINT N/A and SATCON 40kn (at
0430UTC).
While some environmental influences remain conducive for development- upper
level divergence poleward, low vertical wind shear (NW at 12kn from CIMSS) and
warm waters (29C). These are offset by proximity to the island of Dolok, and
movement into a much drier environment that is now apparent. Model guidance is
in agreement that the circulation will continue to weaken.
There is broad model consensus for movement to the west northwest as the
weakening system is steered by the persistent low level southeasterly trade
flow.