90S INVEST 210514 1800 .5S 77.0E SHEM 15 0
SIO: INVEST 90S
Moderator: S2k Moderators
Re: SIO: INVEST 90S
The Southwest Indian Ocean has a trade wind pattern west of 70°E and a large area of low pressure
east of this boundary within which a low pressure circulation is detectable. The 0402UTC ASCAT
swath allows to estimate a circulation between poorly defined in the northern part and winds of
about 30kt in the southwest quadrant by gradient effect. At 09UTC, the center of circulation is
localizable towards 5.5S/75.5E under a burst of convection. The strong convective activity over the
basin is mainly concentrated close to this circulation and more spread out at the eastern limit of our
basin.
Currently in an unfavorable sheared environment, the circulation will move over the next two days
into an area where the shear is more favorable. A 48 hour window for intensification is expected
which will allow the circulation to consolidate. Winds of around 35kt are possible in the southern
sector of the circulation due to the gradient effect with the high pressure present further south. Then
on Tuesday, the wind shear and the intrusion of dry air should hinder the continuation of the
intensification leaving the system close to the threshold of moderate tropical storm.
The risk of formation of a moderate tropical storm is moderate from Tuesday
east of this boundary within which a low pressure circulation is detectable. The 0402UTC ASCAT
swath allows to estimate a circulation between poorly defined in the northern part and winds of
about 30kt in the southwest quadrant by gradient effect. At 09UTC, the center of circulation is
localizable towards 5.5S/75.5E under a burst of convection. The strong convective activity over the
basin is mainly concentrated close to this circulation and more spread out at the eastern limit of our
basin.
Currently in an unfavorable sheared environment, the circulation will move over the next two days
into an area where the shear is more favorable. A 48 hour window for intensification is expected
which will allow the circulation to consolidate. Winds of around 35kt are possible in the southern
sector of the circulation due to the gradient effect with the high pressure present further south. Then
on Tuesday, the wind shear and the intrusion of dry air should hinder the continuation of the
intensification leaving the system close to the threshold of moderate tropical storm.
The risk of formation of a moderate tropical storm is moderate from Tuesday
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Re: SIO: INVEST 90S
Within the near-equatorial area, a wide clockwise circulation lies over the center of the basin,
generated by the tropical wave activity over the last days. Convection is concentrated within this
area but it significantly weakened since this morning, following the diurnal cycle. Sat animations
suggest a closed clockwise circulation but wtill ill-defined on its northern semi-circle, centered in
the South-East of the Chagos archipelago near 7.5S/73.3 at 09Z. Wind is estimated at 25kt within
the southern semi-circle.
From tomorrow afternoon and until Wednesday night, the weak system will encounter conducive
upper conditions : no wind shear and a moderate upper divergence, especially on the polar side.
However, mid-level dry air and a clear lack of equatorward low-level convergence should hinder
the consolidation of a symmetrical circulation. The last model runs thus suggest a decrease in their
estimated cyclogensis risk.
Thursday, a strong North-Westerly shear quickly sets up ahead of a mid-latitudes upper trough. This
trough should interacts with the South-Eastern tip of the low-pressure area and lead to the formation
of a baroclinic low in the South-East of Rodrigues island and North of 25S.
The risk of formation of a moderate tropical storm is low from Tuesday until Wednesday
night in the South-West of the Chagos archipelago.
generated by the tropical wave activity over the last days. Convection is concentrated within this
area but it significantly weakened since this morning, following the diurnal cycle. Sat animations
suggest a closed clockwise circulation but wtill ill-defined on its northern semi-circle, centered in
the South-East of the Chagos archipelago near 7.5S/73.3 at 09Z. Wind is estimated at 25kt within
the southern semi-circle.
From tomorrow afternoon and until Wednesday night, the weak system will encounter conducive
upper conditions : no wind shear and a moderate upper divergence, especially on the polar side.
However, mid-level dry air and a clear lack of equatorward low-level convergence should hinder
the consolidation of a symmetrical circulation. The last model runs thus suggest a decrease in their
estimated cyclogensis risk.
Thursday, a strong North-Westerly shear quickly sets up ahead of a mid-latitudes upper trough. This
trough should interacts with the South-Eastern tip of the low-pressure area and lead to the formation
of a baroclinic low in the South-East of Rodrigues island and North of 25S.
The risk of formation of a moderate tropical storm is low from Tuesday until Wednesday
night in the South-West of the Chagos archipelago.
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Re: SIO: INVEST 90S
MFR no longer predicts development
In the near-equatorial area, the area of low pressure monitored over the last few days is now in the
form of a large Area of Disturbed Weather stretched between 11S/63E and 13S/72E. Satellite
animations, the latest scatterometer passes and the CIMSS vorticity analyses at 850 hPa show that 2
areas of preferential vorticity exist at each end of this low pressure system. Convective activity is
essentially present in the easternmost zone within the deepest warm and humid air. Winds are
estimated at 25/30 kt on the southern edge of this Area of Disturbed Weather.
The current lack of low levels convergence has been the main detrimental factor of development
during the last 24 hours. This will become even more pronounced tomorrow with an interaction
with a mid-latitude trough that will weaken the low-level convergence on the south side and drain
southwards a large part of the humid tropical air associated with the easternmost vorticity zone.
This warm advection will participate in the second part of the week to a cyclogenesis with mainly
baroclinic characteristics in the South-East of the Mascarene Islands between 20S and 30S. From
the initial Disturbed Zone, only the westernmost vortex will remain, which will have no potential to
develop in an environment that is too dry in the middle troposphere and sheared.
There is no longer any risk of a moderate tropical storm forming over the basin during the
next 5 days.
form of a large Area of Disturbed Weather stretched between 11S/63E and 13S/72E. Satellite
animations, the latest scatterometer passes and the CIMSS vorticity analyses at 850 hPa show that 2
areas of preferential vorticity exist at each end of this low pressure system. Convective activity is
essentially present in the easternmost zone within the deepest warm and humid air. Winds are
estimated at 25/30 kt on the southern edge of this Area of Disturbed Weather.
The current lack of low levels convergence has been the main detrimental factor of development
during the last 24 hours. This will become even more pronounced tomorrow with an interaction
with a mid-latitude trough that will weaken the low-level convergence on the south side and drain
southwards a large part of the humid tropical air associated with the easternmost vorticity zone.
This warm advection will participate in the second part of the week to a cyclogenesis with mainly
baroclinic characteristics in the South-East of the Mascarene Islands between 20S and 30S. From
the initial Disturbed Zone, only the westernmost vortex will remain, which will have no potential to
develop in an environment that is too dry in the middle troposphere and sheared.
There is no longer any risk of a moderate tropical storm forming over the basin during the
next 5 days.
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