EXCLUSIVE EXPLAINER| Cyclone Arnab Wind Speed: IMD marks 155-165 kmph vs JTWC’s 222 kmph – Know the Truth!

Bhubaneswar: In Odisha, Tuesday morning witnessed a flurry of social media activity and intense blogging debates over the wind speed of Cyclone Arnab. For online hype-mongers, the temptation invariably lies in headlining the biggest, most alarming numbers.

In the ensuing melee, the average resident tracking the approach of the storm was left deeply confused. Many independent digital forecasters picked up an international broadcast from the Joint Typhoon Warning Center (JTWC), warning of a catastrophic, Category 4-equivalent monster packing winds of 120 knots (222 km/h).

Yet, the state governments of Odisha and Andhra Pradesh, alongside the Special Relief Commissioner (SRC) of Odisha, have strongly urged the public not to trust unverified sources. They maintain that the official India Meteorological Department (IMD) bulletin presents the definitive ground reality: a Very Severe Cyclonic Storm with sustained winds of 155 to 165 km/h.

This stark numerical gap leaves the common man facing a critical dilemma: Which forecast is correct, how strong is the storm hitting my neighborhood, and who should I trust?

The short answer is comforting: Both agencies are looking at the exact same storm, and neither is wrong. The discrepancy is not a mathematical blunder, but a result of different tracking methods.

Here is an elaborate, layman-friendly breakdown of the atmospheric science behind the numbers, why the agencies differ, and what the "actual" wind means for your safety.

The Stop-Watch Difference: 1-Minute vs. 3-Minute Winds

The primary source of confusion comes down to a fundamental rule of meteorological bookkeeping: the averaging time period.

THE WIND MEASUREMENT GAP

• JTWC (USA)
• Standard Time-Frame: 1-Minute Sustained
• Averaging Effect: Captures brief, raw peaks
• IMD (India)
• Standard Time-Frame: 3-Minute Sustained
• Averaging Effect: Smooths out sudden spikes

 

Imagine standing on a beach as a powerful gust of wind hits you. The wind does not blow at a perfectly constant speed; it surges, dips, and slams in erratic pulses.

The American Method (JTWC)

The Joint Typhoon Warning Center (JTWC), a U.S. military command that tracks global tropical cyclones, uses a 1-minute sustained wind standard. Their computers look at a 60-second window and record the average speed. Because one minute is a short time frame, it easily captures the raw, brief surges of the storm's maximum energy. This is why the JTWC clocks Cyclone Arnab at a roaring 222 km/h.

The Indian Method (IMD)

The India Meteorological Department (IMD), along with most nations under the World Meteorological Organization (WMO) framework, utilizes a 3-minute sustained wind standard. The IMD requires the wind to maintain its velocity over a longer, three-minute stretch to count as the "sustained" speed.

Because a three-minute window forces the highs and lows of the wind pulses to blend together, the mathematical average naturally drops. The brief, terrifying spikes are ironed out by the clock. Consequently, the IMD records Arnab’s sustained speed at a lower baseline of 155 to 165 km/h.

The Takeaway: If you mathematically convert the JTWC’s 1-minute wind down to a 3-minute average using standard atmospheric reduction factors, the American forecast drops to roughly 195 km/h. This lines up closely with the IMD's peak gusting value of 185 km/h, proving the two agencies see the same physical threat.

The Satellite Paradox: The Battle of DEMS vs. PGTW

The confusion deepens when looking at the specialized satellite ratings inside the technical bulletins. The text reveals that the American satellite analysis (labeled PGTW) rated the storm as a T6.0 (115 knots), while the Indian analysis (labeled DEMS) rated it much lower at a T4.5 (77 knots).

How can expert meteorologists looking at the same satellite images come up with such drastically different assessments? The answer lies in how they interpret hidden data.

THE SATELLITE INTERPRETATION SPLIT

·         DEMS (IMD)

o    Data Source Used: Standard Infrared

o    Resulting Verdict: Conservative, steady curve

·         PGTW (JTWC)

o    Data Source Used: Microwave Pass

o    Resulting Verdict: Aggressive, exposed inner eye

1. The X-Ray Vision of Microwave Imagery

During the afternoon of October 27, Cyclone Arnab was wrapping itself in thick, high-altitude clouds. To standard infrared satellites, the storm's eye appeared to be filling up and weakening. The IMD (DEMS) tracking rules, which rely on these standard visual cloud patterns, held a conservative estimate.

However, the JTWC (PGTW) caught a lucky break: a specialized military satellite (SSMIS microwave pass) flew directly over the storm. Microwave sensors act like an X-ray, slicing right through high-level cloud covers. This scan revealed that beneath the messy upper clouds, Arnab had constructed a tightly wound, highly organized inner eyewall. The American forecasters saw this hidden core and immediately escalated their wind estimate upward, while the local framework maintained a steadier, more traditional curve.

2. The "Land Proximity" Safety Brake

The IMD utilizes strict, automated "holding constraints" when a cyclone gets close to land. These rules prevent a storm's official rating from jumping or plummeting too drastically within a short 6-to-12-hour window. This safety brake ensures that public warnings do not fluctuate wildly, causing panic or complacency. The JTWC, operating globally without the responsibility of issuing local evacuation mandates, relaxes these constraints to focus purely on real-time maximum physical potential.

Real-World Math: What is the "Actual" Wind Speed?

If a tree is about to fall on a power line in Malkangiri, it does not care about international data standards. The common man simply needs to know: What is the actual force hitting the ground?

The reality is that both numbers are real; they just measure different structural risks.

WHICH NUMBER SHOULD YOU USE?

·         For roof resilience, structural flying debris, and immediate danger:

o    Recommended Metric: IMD Gusting Speed (185 km/h) / JTWC Speed (222 km/h)

·         For long-term structural engineering, walls, and bridges:

o    Recommended Metric: IMD Sustained Speed (155–165 km/h)

·         The 155–165 km/h Number (IMD Sustained): This represents the relentless, crushing weight of the wind that will blow continuously against buildings, bridges, and mobile towers for hours at a time. Indian infrastructure, coastal embankments, and emergency shelters are engineered explicitly to withstand these 3-minute sustained forces.

·         The 185–222 km/h Number (IMD Gusts / JTWC Peak): This represents the sudden, explosive punches of wind that happen within the storm bands. These temporary, fraction-of-a-second blasts are what violently rip corrugated tin roofs off houses, snap centuries-old banyan trees, and transform loose objects into lethal projectiles.

The Action Plan for the Ground

As Cyclone Arnab makes its final approach toward the south Odisha border, the common man should ignore the mathematical tug-of-war between agencies and focus on the overlapping reality of their warnings.

The core agreement between the IMD and JTWC is absolute: Arnab is a dangerous, top-tier tropical system. Whether measured by Indian or American clocks, the storm carries enough kinetic energy to cause widespread electrical outages, flash floods, and structural damage across the Red Alert zones of Malkangiri, Koraput, and Rayagada throughout Wednesday.

Residents are urged to stay indoors, secure all loose property, and rely strictly on the tactical, district-level safety directives issued by the local administration.

Also Read: EXCLUSIVE| Cyclone Arnab Clouds to Burst on Malkangiri Skylines by 2 AM Tonight!