This is storm THELMA that was active in 1999 in the S. Indian region with maximum winds of 259 km/h.

What was the maximum intensity of the storm?

Max Wind: 259 km/h. Min Pressure: hPa.

storm THELMA (1999) - Track and intensity details

Name: storm THELMA
Start: 1998-12-01
End: 1998-12-15
Location: S. Indian

THELMA (1999)

Storm Code: 1998335S12138 | Region: S. Indian
Active from 01/12/1998 to 15/12/1998 (15 days)

250 km/h

1-min Wind (JTWC)

Level 17

222 km/h

10-min Wind (BOM)

Level 17

920 hPa

Min Pressure

2,967 km

Distance

Forecast Agencies

Agency	Max Intensity	Trajectory	Energy	highest_classification
WMO (International)	222	920	83	2,776	65.17	124.44	Level 17 - Super Typhoon
BOM (Australia)	222	920	113	2,796	65.17	124.44	Level 17 - Super Typhoon
NEUMANN	259	920	113	2,967	88.46	187.83	Level 17 - Super Typhoon
JTWC	250	~	91	2,285	97.13	204.98	Level 17 - Super Typhoon

Agency

Max Intensity

Trajectory

Energy

highest_classification

Max Wind (km/h)

Min Pressure (hPa)

Number of points

Distance (km)

ACE (10⁴ (km/h)²)

PDI (10⁶ (km/h)³)

WMO (International)

222

920

2,776

65.17

124.44

Level 17 - Super Typhoon

BOM (Australia)

222

920

113

2,796

65.17

124.44

Level 17 - Super Typhoon

NEUMANN

259

920

113

2,967

88.46

187.83

Level 17 - Super Typhoon

JTWC

250

2,285

97.13

204.98

Level 17 - Super Typhoon

Advanced Meteorological Indices by Agency Automatically calculated from raw data

WMO (International) RI

Energy
ACE (10⁴ (km/h)²)	65.17	Very High
PDI (10⁶ (km/h)³)	124.44
Intensification / Weakening
Max Wind Gain/Step	+19 km/h
Max Wind Gain/24h	+93 km/h	RI
Max Wind Loss/Step	-28 km/h
Pressure Variation
Max Pressure Drop/Step	-10 hPa
Max Pressure Drop/24h	-40 hPa	RI
Max Pressure Rise/Step (weakening)	+10 hPa
Movement & Duration
Avg Movement Speed	8.3 km/h
Tracking Time	336h (14 days)
Time as TD+ (≥34kt)	132h (5.5d)
Time as Storm+ (≥64kt)	99h (4.1d)
Peak Intensity & Range
Peak Intensity	16:00 08/12/1998 -11.5°N, 129.4°E
Latitude	-20.4°N – -9.2°N (11.2°)
Longitude	119.5°E – 138°E (18.5°)

BOM (Australia) RI

Energy
ACE (10⁴ (km/h)²)	65.17	Very High
PDI (10⁶ (km/h)³)	124.44
Intensification / Weakening
Max Wind Gain/Step	+19 km/h
Max Wind Gain/24h	+93 km/h	RI
Max Wind Loss/Step	-28 km/h
Pressure Variation
Max Pressure Drop/Step	-10 hPa
Max Pressure Drop/24h	-40 hPa	RI
Max Pressure Rise/Step (weakening)	+10 hPa
Movement & Duration
Avg Movement Speed	8.3 km/h
Tracking Time	336h (14 days)
Time as TD+ (≥34kt)	132h (5.5d)
Time as Storm+ (≥64kt)	99h (4.1d)
Peak Intensity & Range
Peak Intensity	16:00 08/12/1998 -11.5°N, 129.4°E
Latitude	-20.1°N – -9.1°N (11°)
Longitude	119.4°E – 138°E (18.6°)

NEUMANN RI

Energy
ACE (10⁴ (km/h)²)	88.46	Very High
PDI (10⁶ (km/h)³)	187.83
Intensification / Weakening
Max Wind Gain/Step	+19 km/h
Max Wind Gain/24h	+102 km/h	RI
Max Wind Loss/Step	-28 km/h
Pressure Variation
Max Pressure Drop/Step	-8 hPa
Max Pressure Drop/24h	-40 hPa	RI
Max Pressure Rise/Step (weakening)	+10 hPa
Movement & Duration
Avg Movement Speed	8.8 km/h
Tracking Time	336h (14 days)
Time as TD+ (≥34kt)	183h (7.6d)
Time as Storm+ (≥64kt)	105h (4.4d)
Peak Intensity & Range
Peak Intensity	19:00 08/12/1998 -11.6°N, 129.2°E
Latitude	-21°N – -9.1°N (11.9°)
Longitude	119.3°E – 138°E (18.7°)

JTWC RI

Energy
ACE (10⁴ (km/h)²)	97.13	Very High
PDI (10⁶ (km/h)³)	204.98
Intensification / Weakening
Max Wind Gain/Step	+28 km/h
Max Wind Gain/24h	+120 km/h	RI
Max Wind Loss/Step	-24 km/h
Movement & Duration
Avg Movement Speed	8.5 km/h
Tracking Time	270h (11.3 days)
Time as TD+ (≥34kt)	216h (9d)
Time as Storm+ (≥64kt)	108h (4.5d)
Peak Intensity & Range
Peak Intensity	19:00 08/12/1998 -11.6°N, 129.2°E
Latitude	-21°N – -8.8°N (12.2°)
Longitude	119.4°E – 133.9°E (14.5°)

Advanced Indices Legend

ACE: Accumulated Cyclone Energy - measures total storm activity

PDI: Power Dissipation Index - measures potential destructiveness

RI: Rapid Intensification - when wind increases >=30 kt/24h or pressure drops >=30 hPa/24h

Countries with Direct Landfall

🏳️ Australia

WMO 139 km/h Level 13

-14.70°, 125.20° 1998-12-10 20:59:17

BOM 139 km/h Level 13

-11.33°, 136.63° 1998-12-01 20:29:45

NEUMANN 124 km/h Level 12

-11.30°, 136.66° 1998-12-01 20:06:23

JTWC 220 km/h Level 17

-14.66°, 125.25° 1998-12-10 19:38:47

Values are interpolated at landfall time and may differ from actual data.

Index	Meaning	Formula / Condition	Classification
ACE Accumulated Cyclone Energy	Accumulated Cyclone Energy. Measures the total energy generated by the storm during its lifetime. Only counts reports with wind ≥ 35 kt (TS level or higher).	`ACE = Σ(V_max²) / 10&sup4;` Unit: 10⁴ kt²	< 2: Low 2-6: Medium 6-15: High ≥ 15: Very High
PDI Power Dissipation Index	Power Dissipation Index. More sensitive than ACE to extremely strong storms due to using cubic power. Reflects potential destructive power.	`PDI = Σ(V_max&sup³;) / 10&sup6;` Unit: 10⁶ kt³	Higher value = greater cumulative destructive power
RI Rapid Intensification	Rapid Intensification - storm strengthens suddenly in a short time. Very dangerous as it is difficult to forecast and causes surprise for prevention efforts.	Wind increase ≥ 30 kt/24h or Pressure drop ≥ 30 hPa/24h	Has RI or Fast increase (≥20kt)
Max wind gain/step	Maximum wind increase between 2 consecutive reports (usually 6 hours apart). Shows the fastest local intensification rate.	`max(V_i+1 - V_i)` Unit: kt (km/h)	Positive value = storm strengthening
Max wind gain/24h	Maximum wind increase in a 24-hour window. Main criterion for determining Rapid Intensification (RI).	`max(V_t+24h - V_t)` RI if ≥ 30 kt/24h	≥ 30kt: RI ≥ 20kt: Fast
Max wind loss/step	Maximum wind weakening between 2 consecutive reports. Shows at which stage the storm weakened fastest.	`max(V_i - V_i+1)` Unit: kt (km/h)	Positive value = storm weakening
Max pressure drop/step	Maximum pressure drop between 2 consecutive reports. Pressure decrease = storm center strengthening. Reflects local deepening rate.	`max(P_i - P_i+1)` Unit: hPa	Higher value = faster strengthening
Max pressure drop/24h	Maximum pressure drop in a 24-hour window. Important index for evaluating explosive deepening / explosive intensification.	`max(P_t - P_t+24h)` Explosive if ≥ 30 hPa	≥ 30hPa: RI ≥ 20hPa: Strong
Max pressure rise/step	Maximum pressure rise between 2 consecutive reports. Pressure increase = storm weakening. Large value indicates rapid weakening (due to terrain interaction, landfall, etc.).	`max(P_i+1 - P_i)` Unit: hPa	Higher value = faster weakening
Average moving speed	Average moving speed of the storm center during the entire monitoring period by that agency.	`V_avg = S_total / T_total` Unit: kt (km/h)	Slow-moving storms (<15 km/h) usually cause prolonged heavy rain
Monitoring duration	Total time from first report to last report of that agency.	`T = t_end - t_start` Unit: hours (days)	Different agencies may monitor for different durations
TS+ Duration	Total hours with average wind ≥ 34 kt (Tropical Storm level or higher). Reflects how long the storm maintained significant intensity.	Average wind ≥ 34 kt	Longer storm = greater total damage
TY+ Duration	Total hours with average wind ≥ 64 kt (Typhoon level or higher). Storms maintaining this level longer have much greater destructive power.	Average wind ≥ 64 kt	Longer time at Typhoon level = more dangerous
Peak Intensity	Time and location (lat, lon) when the storm reached maximum wind according to each agency. Helps identify where the storm was strongest.	V_max = max(V_i)	Peak location helps assess danger for nearby areas
Latitude / Longitude	Spatial range of activity by latitude and longitude. Shows whether the storm affected area is wide or narrow.	min-max(lat), min-max(lon)	Large range = long trajectory, wide impact

Index

Meaning

Formula / Condition

Classification

ACE
Accumulated Cyclone Energy

Accumulated Cyclone Energy. Measures the total energy generated by the storm during its lifetime. Only counts reports with wind ≥ 35 kt (TS level or higher).

ACE = Σ(V_max²) / 10&sup4;
Unit: 10⁴ kt²

< 2: Low
2-6: Medium
6-15: High
≥ 15: Very High

PDI
Power Dissipation Index

Power Dissipation Index. More sensitive than ACE to extremely strong storms due to using cubic power. Reflects potential destructive power.

PDI = Σ(V_max&sup³;) / 10&sup6;
Unit: 10⁶ kt³

Higher value = greater cumulative destructive power

RI
Rapid Intensification

Rapid Intensification - storm strengthens suddenly in a short time. Very dangerous as it is difficult to forecast and causes surprise for prevention efforts.

Wind increase ≥ 30 kt/24h or Pressure drop ≥ 30 hPa/24h

Has RI or
Fast increase (≥20kt)

Max wind gain/step

Maximum wind increase between 2 consecutive reports (usually 6 hours apart). Shows the fastest local intensification rate.

max(V_i+1 - V_i)
Unit: kt (km/h)

Positive value = storm strengthening

Max wind gain/24h

Maximum wind increase in a 24-hour window. Main criterion for determining Rapid Intensification (RI).

max(V_t+24h - V_t)
RI if ≥ 30 kt/24h

≥ 30kt: RI
≥ 20kt: Fast

Max wind loss/step

Maximum wind weakening between 2 consecutive reports. Shows at which stage the storm weakened fastest.

max(V_i - V_i+1)
Unit: kt (km/h)

Positive value = storm weakening

Max pressure drop/step

Maximum pressure drop between 2 consecutive reports. Pressure decrease = storm center strengthening. Reflects local deepening rate.

max(P_i - P_i+1)
Unit: hPa

Higher value = faster strengthening

Max pressure drop/24h

Maximum pressure drop in a 24-hour window. Important index for evaluating explosive deepening / explosive intensification.

max(P_t - P_t+24h)
Explosive if ≥ 30 hPa

≥ 30hPa: RI
≥ 20hPa: Strong

Max pressure rise/step

Maximum pressure rise between 2 consecutive reports. Pressure increase = storm weakening. Large value indicates rapid weakening (due to terrain interaction, landfall, etc.).

max(P_i+1 - P_i)
Unit: hPa

Higher value = faster weakening

Average moving speed

Average moving speed of the storm center during the entire monitoring period by that agency.

V_avg = S_total / T_total
Unit: kt (km/h)

Slow-moving storms (<15 km/h) usually cause prolonged heavy rain

Monitoring duration

Total time from first report to last report of that agency.

T = t_end - t_start
Unit: hours (days)

Different agencies may monitor for different durations

TS+ Duration

Total hours with average wind ≥ 34 kt (Tropical Storm level or higher). Reflects how long the storm maintained significant intensity.

Average wind ≥ 34 kt

Longer storm = greater total damage

TY+ Duration

Total hours with average wind ≥ 64 kt (Typhoon level or higher). Storms maintaining this level longer have much greater destructive power.

Average wind ≥ 64 kt

Longer time at Typhoon level = more dangerous

Peak Intensity

Time and location (lat, lon) when the storm reached maximum wind according to each agency. Helps identify where the storm was strongest.

V_max = max(V_i)

Peak location helps assess danger for nearby areas

Latitude / Longitude

Spatial range of activity by latitude and longitude. Shows whether the storm affected area is wide or narrow.

min-max(lat), min-max(lon)

Large range = long trajectory, wide impact

THELMA (1999)

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Indices Legend

Advanced Meteorological Indices by Agency Automatically calculated from raw data

Advanced Indices Legend

Countries with Direct Landfall

THELMA

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THELMA (1999)

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Comparison Storms 0

Weather Agencies (4 sources)

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Track List (0 points)

Wind Intensity Chart

Quick Stats

Agency Data Comparison

Indices Legend

Advanced Meteorological Indices by Agency Automatically calculated from raw data

Advanced Indices Legend

Countries with Direct Landfall

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THELMA

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