Singapore Sumatra Squall Centre

PROD2 SSSC SSRR
DHC LCA LTCA HMC

***THIS IS A POST-INCIDENT REPORT, NO ACTION IS NEEDED***

Sumatra Squall Reanalysis Report
SSSC Singapore Sumatra Squall Centre
2235 SGT Sun May 31 2026

REANALYSIS REPORT ON SQUALL LINE HERMINE (SQL-11).

Under the continued influence of prevailing westerly low level winds, disorganized area of shower and thunderstorm activity developed over North Riau, moved eastwards towards the Straits of Malacca at around midnight of May 30.
At around 2am SGT of May 30, radar observation indicated the continued development of the system, and a squall line is developing offshore of Johor, Malaysia. At approximately 2;30am SGT, it made landfall over Johor and continued inland over the region, affecting Singapore, north of Tanjung Balai Karimun and Batam-Bintan Islands.
Maximum winds of 59.3kph was recorded in Johor Bahru Airport, with numerous 45-50kph readings across Singapore, hence Squall Line Hermine was a strong squall line.

Hermine continued eastwards towards the open South China Sea, and weakened slowly over the diurnal minimum into the afternoon.

Report by Ryan

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DHC LCA LTCA HMC

***THIS IS A POST-INCIDENT REPORT, NO ACTION IS NEEDED***

Sumatra Squall Reanalysis Report
SSSC Singapore Sumatra Squall Centre
1743 SGT Fri May 29 2026

REANALYSIS REPORT ON POTENTIAL SQUALL LINE EIGHT (PSL-8), SQUALL LINES FIFI (SQL-9) AND GUS (SQL-10).

..POTENTIAL SQUALL LINE EIGHT (PSL-8)...
The disorganized area of shower and thunderstorm activity first developed offshore of Eastern Jambi at 27 May at around 8am SGT. Under the influence of favorable westerly low level winds, this area of convection started to show some signs of organization just west of Singkep-Lingga Islands. By around 9am SGT, it made landfall over the island with winds of 20.4kph.
The system then departed Singkep-Lingga Islands and started to weaken under the diurnal minimum, with no further intensification.

..SQUALL LINE FIFI (SQL-9)...
Under the prevailing westerlies winds, a group of disorganized area of shower and thunderstorm activity moved offshore of Northeastern Riau into the Straits of Malacca. At approximately 5-6am SGT, radar observations indicate that this area of convection have further organized into a developing squall system, just west of Tanjung Balai Karimun. Surface observations over the region only recorded winds of ~25kph, but as the system accelerated across Southwest Singapore and Batam-Bintan Islands, winds of ~40kph was recorded at Pasir Panjang, with the highest winds of 42.6kph recorded at Batam Airport.
Fifi continued southeast and slowly weakened throughout the afternoon of May 28.

..SQUALL LINE GUS (SQL-10)...
Another round of fast moving eastwards area of convection appeared over the Straits of Malacca at about 4am SGT of today. It continued eastwards towards Johor and started to show signs of rapid organization just offshore. Radar imagery at 5am SGT confirmed the development of Squall Line Gus, the 10th of the season. Gus made landfall over Johor, Singapore and Batam-Bintan Islands, with ~40kph across Johor, Singapore and parts of Batam Island. Maximum winds of 42.6kph was recorded on Tanjungpinang. Gus continued southeast and doubled in size as it merged with another developing thunderstorm complex to the south.

Report by Ryan

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DHC LCA LTCA HMC

Squall Line Outlook
SSSC Singapore Sumatra Squall Centre
1128 SGT Fri May 22 2026

1. A vigorous area of shower and thunderstorm activity is currently active north of Belitung Islands offshore of Pontianak, West Kalimantan. Latest satellite and radar imagery indicate that the apparent line of thunderstorm is showing rapid signs of organization, but radar imagery at this time still shows haphazard flare-ups of thunderstorm activity within this line of convergence.
Environmental conditions are still favorable for further development before the minimum diurnal cycle later in the afternoon, and a further increase in organization could lead to the development of a potential squall system.

*Formation chance within the next 3 hours...low...30 percent.
*Formation chance within the next 6 hours...medium...50 percent.

======
SUMMARY OF WATCHES & WARNINGS:
*A Squall Warning Is In Effect For:
NIL

*A Squall Watch Is In Effect For:
- Pontianak Regency

Forecaster Ryan

PROD2 SSSC SSRR
DHC LCA LTCA HMC

***THIS IS A POST-INCIDENT REPORT, NO ACTION IS NEEDED***

Sumatra Squall Reanalysis Report
SSSC Singapore Sumatra Squall Centre
1441 SGT Wed May 20 2026

REANALYSIS REPORT ON SQUALL LINE EUGENE (SQL-7).

Disorganized area of shower and thunderstorm activity first developed over Peninsula Malaysia, moving eastwards towards the open South China Sea. Under the influence of favorable low level winds, this area of convection exited Kuantan, Malaysia and started to develop offshore.

At around 4am SGT, the convection seen on radar has showed signed of organization, and a squall line appear to have formed, and was given the name Eugene, the 7th squall system of the 2026 Sumatra Squall season. There were no avaialble surface observations, except for an observation at Kuantan at 18.5kph, but is not representative of the squall intensity due to further development offshore.

By 7am SGT, Eugene started to rapidly weaken under the influence of dry air seen on satellite imagery, and dissipated at around 8am SGT just before the Riau Archipelago.

Report by Ryan

PROD2 SSSC SSRR
DHC LCA LTCA HMC

***THIS IS A POST-INCIDENT REPORT, NO ACTION IS NEEDED***

Sumatra Squall Reanalysis Report
SSSC Singapore Sumatra Squall Centre
0038 SGT Thu May 14 2026

REANALYSIS REPORT ON SQUALL LINE DEBBIE (SQL-6).

Disorganized area of shower and thunderstorm activity first developed over Northern Riau under the influence of the leading start of a Westerly Wind Burst (WWB) event over the Equatorial Indian Ocean. Under this influence, the area of convection moved eastwards towards Northeast Riau and adjoining Straits of Malacca at around 11pm SGT on May 12.

The system continued to show signs of organization, and at around 2am SGT of May 13, Squall Line Debbie was determined to have formed over the Straits of Malacca off the coast of Malacca City. Radar imagery by then indicated strong easterly mid level shear impacting the system, while the squall continued eastwards under the influence of westerly low level winds. Debbie went on to affect Johor and Singapore in the predawn hours at around 7am SGT.

Maximum winds of 41.9kph was recorded in Pasir Panjang, Singapore and a 37kph PWS reading was recorded in Tanjung Balai Karimun, Indonesia.

Report by Ryan

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DHC LCA LTCA HMC

Sumatra Squall Monthly Analysis
SSSC Singapore Sumatra Squall Centre
2300 SGT Thu May 7 2026

Monthly Sumatra Squall Statistics Report for April, season 2026.

Summary:
April is a below average month, with only 2 potential squall systems or stronger that developed in the month. The initial prediction of 2-3, which was below average, verified. With the positive phase of Madden-Julian Oscillation (MJO) was largely within our region, easterlies were dominant throughout the month, which has suppressed squall activity.

April featured only 2 systems, of which only 1 was a mature squall line. Four (PSL-4) developed on Apr 5 and Cosmo (SQL-5) on Apr 7. The highest winds were Cosmo at 55.6kph recorded by a METAR in Tanjung Balai Karimun, Indonesia.

Climatological Average:
April climatologically produces 5.11 (9.46%) potential squall systems or stronger for the month, with 8.52 being above average, and 1.70 being below average. This April was below average of 2, and is the slowest April since the 2023 Sumatra Squall season, but consistent with the earlier years between 2017-21

Outlook:
May, based on climatological averages, should continue to see a gradual increase in squall numbers for the 2026 Sumatra Squall season, which will then welcome the 1st peak of squall season, which produces 5.89 potential squall systems or stronger for the month. Considering climatological predictions, we are expecting an average month, with 5-7 systems developing.

Prognostic Reasoning:
Low level winds
GFS, AIGFS, ECMWF, AIFS and CMC all indicate a Westerly Wind Burst (WWB) event happening on the 2nd week of the month. Ensemble models support the scenario and transcends into our region. All climate models support the same scenario.

Rainfall anomalies
GFS, AIGFS, ECMWF, AIFS and CMC are all indicating very high PWAT anomalies throughout the month, which is supported by all major ensemblist models. The exception being ECMWF and GEFS indicating possible dry air incursion at the start of 3rd week. Climate models are bipolar, with CFS and C3S being unusually dry, while the rest of the model suite calls for average to above average rainfall.

Overall
Owing to the above, westerlies are expected to increase ahead of the start of the WWB event, and is expected to retain its background state throughout the month as we transit into the Southwest Monsoon. Depending on if a large cyclone forms in the Bay of Bengal, there is a higher chance of dry air intrusion on week 3 as proposed by Euro and American ensembles, which I will be lowering the forecast for this period. Hence, we are expecting an average month.

Next message: by Jun 7.

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DHC LCA LTCA HMC

***THIS IS A POST-INCIDENT REPORT, NO ACTION IS NEEDED***

Sumatra Squall Reanalysis Report
SSSC Singapore Sumatra Squall Centre
1826 SGT Tue Apr 7 2026

REANALYSIS REPORT ON POTENTIAL SQUALL LINE FOUR (PSL-4) AND SQUALL LINE COSMO (SQL-5).

..POTENTIAL SQUALL LINE FOUR (PSL-4)...
A area of shower and thunderstorm activity first developed over Central Riau, east of Pekanbaru, moved eastwards towards Eastern Riau at midnight SGT of Apr 6. Under the influence of favorable westerly low level winds, this area of convection started to show signs of organization seen on radar imagery.
At about 1am SGT, the associated convective activity has continued to show slow signs of organization while over the Straits of Malacca. However, by the time the system is making landfall over Peninsula Malaysia, radar imagery still continued to show the overall disorganization of the system, and was not considered to be a squall line.

Upon reanalysis however, it was considered that a potential squall system would have formed, and was given the 4th deisgnator for the 2026 Sumatra Squall season. Four continued towards the open South China Sea and slowly weakened thereafter. Maximum winds of 53.7kph was recorded in East Coast Parkway, Singapore.

..SQUALL LINE COSMO (SQL-5)...
Another area of shower and thunderstorm activity developed over Central Riau, moved eastwards under the influence of favorable westerly low level winds, and showed signs of organization over the Straits of Malaccain the early morning of SGT today. Radar imagery indicated by then, a squall line has formed, and Cosmo was the given name, the 5th of the season.

Cosmo continued over Peninsula Malaysia where widespread strong winds were detected across Singapore, Tanjung Balai Karimun and the Batam-Bintan Islands. Maximum winds of 55.6kph was recorded in Tanjung Balai Karimun, Indonesia.

Cosmo continued over the South China Sea and weakened under the influence of the diurnal minimum.

Report by Ryan

MTSR SSSC SSMA CCA
DHC LCA LTCA HMC

***CORRECTIVE TO FORECASTED SQUALL NUMBERS***

Sumatra Squall Monthly Analysis
SSSC Singapore Sumatra Squall Centre
2300 SGT Tur Apr 7 2026

Monthly Sumatra Squall Statistics Report for March, season 2026.

Summary:
March is climatologically the start of the Sumatra Squall season, with an average of 4.63 squalls that develop within this month. However, this March has recorded the least active squall month on record, surpassing the 2024 Sumatra Squall season of 1, to achieve exactly 0 squall line formation this month.

The primary reason was likely attributed to the suppressive phase of the Madden-Julian Oscillation (MJO), additionally with frequent dry air incursion in the region, likely was the contributing factor for the month's demise.

Climatological Average:
March climatologically produces 4.63 (8.57%) potential squall systems or stronger for the month, with 7.35 being above average, and 1.91 being below average. This March was well below average of 0, which is the lowest amount of squall lines that developed on record for the month of March.

Outlook:
April, based on climatological averages, should continue to see a gradual increase in squall numbers for the 2026 Sumatra Squall season, which produces 5.11 potential squall systems or stronger for the month. Considering climatological predictions, we are expecting a below average month, with 2-4 systems developing.

Prognostic Reasoning:
Low level winds
GFS, ECMWF and CMC is indicating westerlies to evacuate eastwards towards the Pacific basin, consistent with the MJO forecast. The ensembles agree on the same scenario. CanSIPS is the only climate model indicating an average or easterly anomaly.

Rainfall anomalies
GFS, ECMWF and CMC deterministic is indicating variable Precipitable Water (PWAT) anomalies moving into April, but generally agree on the lower end of the PAAT anomaly. The ensembles all agree on the deterministic scenario, with the exception of the GEPS indicating an average PWAT anomaly. CFS Weekly and SubC agree on the deterministic and ensemblist scenario, with the CFS being a little more variable. CFS Monthly, C3S, NMME and CanSIPS all suggest below average rainfal.

Overall
Owing to the above, westerlies are expected to depart eastwards consistent with the MJO forecast, but will still remain generally westerly. Rainfall anomalies are expected to remain at below average levels, and continue to remain this way throughout the rest of April. Hence, the current forecast still strongly suggest the continued muted start of the 2026 Sumatra Squall season.

Next message: by May 7.

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DHC LCA LTCA HMC

Sumatra Squall Monthly Analysis
SSSC Singapore Sumatra Squall Centre
2300 SGT Fri Mar 6 2026

Monthly Sumatra Squall Statistics Report for the off-season.

Summary:
The off season this time round is below average, with 4 potential squall systems or stronger developing. The long term average for the off season is 8, despite persistent westerlies and a tropical cyclone developing within our Area of Responsibility (AoR) in November 2025.

The off season featured 4 total systems, which is below average number of squalls that occur during this period. The squalls include Yakovlev (SQL-61) on Dec 2, Zander (SQL-1) on Jan 1, Arnold (SQL-2) on Jan 2 and Blair (SQL-3) on Feb 27. The strongest squall line was Squall Line Yakovlev (SQL-61), at 50.7kph recorded by a SYNOP station.

Climatological Average:
The off season climatologically produces 9.17 (~15%) potential squall systems or stronger for the month, with 10.98 being above average, and 7.36 being below average. This off season is below average of 4.

Outlook:
March, based on climatological averages, sees the start of the normal bounds of the 2026 Sumatra Squall season, where we should start to see the increase in squalls, which produces 4.63 potential squall systems or stronger for the month. Considering climatological predictions, we are expecting a below average month, with 2-3 systems developing.

Prognostic Reasoning:
Low level winds
GFS, ECMWF and CMC is indicating westerlies to evacuate eastwards towards the Pacific basin, consistent with the MJO forecast. The ensembles agree on the same scenario. CanSIPS and C3S is also indicating the same scenario.

Rainfall anomalies
GFS, ECMWF and CMC deterministic is indicating decreasing Precipitable Water (PWAT) anomalies moving into March. The ensembles all agree on the deterministic scenario. CFS Weekly and SubC agree on the deterministic and ensemblist scenario. CFS Monthly, C3S and NMME all suggest below average rainfall, with CanSIPS ironically calling for average rainfall activity.

Overall
Owing to the above, westerlies are expected to depart eastwards consistent with the MJO forecast. Rainfall anomalies are expected to decrease to below average levels. Hence, the current forecast strongly suggest a muted start of the 2026 Sumatra Squall season.

Next message: by Apr 7.

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DHC LCA LTCA HMC

***THIS IS A POST-INCIDENT REPORT, NO ACTION IS NEEDED***

Sumatra Squall Reanalysis Report
SSSC Singapore Sumatra Squall Centre
1733 SGT Fri Feb 27 2026

REANALYSIS REPORT ON SQUALL LINE BLAIR (SQL-3).

A small area of shower and thunderstorm activity first developed over Central Riau, east of Pekanbaru, moved eastwards towards Eastern Riau at midnight SGT of today, Feb 27. Under the influence of favorable westerly low level winds, this area of convection started to show signs of organization seen on radar imagery.
At about 1am SGT, the associated convective activity has coalesced further and a squall line was forming. Hence, advisories were initiated for Squall Line Blair, the 3rd of the 2026 Sumatra Squall season.

Blair continued eastwards towards the open Straits of Malacca and further developed as it made landfall over Singapore at 2:30am SGT, bringing moderate to heavy thundery showers with gusty winds, and affecting Johor and the Batam-Bintan Islands. Maximum winds of 50.0kph was recorded at Tanjungpinang, with other wind observations of 45-49kph in Tanjung Balai Karimun and parts of Western Singapore.

Blair continued eastwards towards the open South China Sea, where it weakened and dissipated over the course of the morning of today.

Report by Ryan