EXCLUSIVE | Bay of Bengal Witnesses Rare Fujiwhara Merger: Cyclone Arnab Swallows Invest 90B, Setting Up Grueling 12+ Hour Landfall Strained over Yanam–Kakinada

Bhubaneswar: GRUELLING TIME for the Yanam–Kakinada coast! A rare meteorological phenomenon has reached its dramatic climax over the Bay of Bengal.

The structural analysis from the India Meteorological Department (IMD) confirms that the complex binary dance – known as the Fujiwhara Effect – has entered a definitive fusion stage, threatening to prolong the landfall of Very Severe Cyclonic Storm "Arnab" to over 12 hours.

According to the IMD bulletin, a low-pressure trough extending up to 3.1 km above mean sea level now runs like a direct atmospheric highway from the Sri Lanka coast straight into the centre of Arnab.

The secondary tropical system, Invest 90B, has officially merged into this trough. Instead of two independent vortices circling each other, the stronger Cyclone Arnab is actively absorbing the smaller system's massive moisture tail, turning it into a relentless rain conveyor belt pinned against the Indian coastline.

While a typical severe cyclone crosses the coast within a clean 5-hour window, this complex vortex merger and the resulting structural drag mean the communities along the Yanam–Kakinada border face an unprecedented, extended battering.

A Rare Tropical Display in the Bay of Bengal

In the tropical history of the Bay of Bengal, finding a pure Fujiwhara merger and deep orbital stall entirely inside this confined basin is an extreme outlier event. Historically, when two low-pressure circulations form within the Bay simultaneously, the dominant storm rapidly tears apart the weaker system before a full orbital rotation can complete.

But this time, the rules changed. Invest 90B was large enough to dynamically anchor and alter Arnab's path without being instantly destroyed. This binary interaction stripped Arnab of its forward momentum, decelerating its translation speed to a crawl of 5 knots or less as it neared the coast. Even as Invest 90B loses its independent identity inside the IMD's mapped trough, its lingering gravitational drag continues to delay Arnab's breakout inland.

The resulting impact is highly dangerous: the storm is lingering right at the coastline, keeping its massive, moisture-heavy northern semicircle positioned over open waters to continuously pump heavy tropical deluges into the shore.

Normal Cyclone vs. Cyclone Arnab

Landfall Feature	Normal VSCS Landfall	Cyclone Arnab (Yanam-Kakinada)
Forward Translation Speed	12 to 15 knots (Fast/Steady)	Decelerating to 5 knots or less
Coast Crossing Duration	3 to 5 hours	12 to 24 hours (Extended battering)
Core Structural Evolution	Fast inland movement leads to rapid frictional decay over dry ground.	Offshore Stalling: The core remains partially over warm shelf waters, feeding it moisture.
Primary Danger Vector	Sudden, extreme peak wind damage followed by a fast exit.	Catastrophic, relentless rainfall and continuous storm surge due to slow motion.

 

Meteorological Evidence & Reasons

• Evidence 1: Collapse of Independent Steering (The Trough Umbilical Cord)

          • The Analysis: The IMD highlights a continuous low-pressure trough extending up to 3.1 km above sea level, connecting the Southwest Bay of Bengal (near Sri Lanka) directly into the core of Very Severe Cyclonic Storm Arnab

          • Why it Delays Landfall: This trough acts like an atmospheric umbilical cord. Instead of Arnab being steered cleanly by the subtropical ridge over China, it is anchored to the massive moisture mass of Invest 90B in the south. The opposing gravitational and rotational pulls create a deadlock, reducing Arnab’s forward speed to a crawl of 5 knots or less just as it hits the shoreline.

• Evidence 2: Massive Structural Footprint Expansion

          • The Analysis: The text explicitly notes that the cyclonic circulation over the Southwest Bay of Bengal has merged into the trough .

          • Why it Delays Landfall: Arnab is actively swallowing and wrapping Invest 90B’s wind fields and cloud canopy into its own structure. This process drastically increases the storm's overall diameter and wind radii. A small, compact storm can cross a coast quickly, but a highly expanded system takes vastly more time for the forward bands, the front eyewall, the eye, and the rear eyewall to completely roll over the same coordinates.

• Evidence 3: Core Reorganization and Rotational "Wobble"

          • The Analysis: As two asymmetrical cyclonic masses fuse together, the center of mass shifting occurs dynamically.

          • Why it Delays Landfall: Before a clean tracking vector can resume, the storm experiences trochoidal oscillations (erratic wobbling or looping). Instead of moving forward in a straight line, the eye meanders and paces back and forth right along the Yanam–Kakinada border. This snake-like creeping motion locks the core eyewall over the same coastal communities for an extended 12+ hours.

How Gruelling It Turns: The Timeline

As VSCS Arnab approaches the Central Andhra Pradesh coast, the landfall sequence will play out in distinct phases:

·         The Pre-Landfall Batter (October 27 evening – October 28 early morning): Arnab slows down to a near-halt just off the coast. Its northern outer gale-force wind radii (extending up to 100 nautical miles or 185 km) will begin sweeping across Visakhapatnam, Kakinada, and Yanam. Massive bands of rain will train repeatedly over the coast as sea conditions become severe, with wave heights peaking near 38 feet.

·         The Extended Landfall Creep (October 28 morning – October 28 night): Driven at a snail's pace by the collapsing binary gradient, the center will slowly creep over the Yanam-Kakinada border zone. The violent inner core (with a core wind radius of 25–30 NM or 55 km) will remain parked over the same coastal strip for 12 to 18 hours. Kakinada, Yanam, and neighboring villages face continuous, destructive winds peaking between 125–140 kmph. The slow-moving eyewall will continuously push walls of water into shallow delta river mouths, causing extensive, catastrophic saltwater storm surge inundation.

Double Whammy: From Open Ocean to Brown Ocean

Cyclone Arnab making landfall over the expansive Godavari River Delta serves as a severe double whammy for Central Andhra Pradesh. Normally, when a tropical system moves inland, cut off from its ocean fuel source, friction causes it to decay rapidly.

However, Arnab is stepping straight onto land primed by the "Brown Ocean Effect." The heavily saturated delta wetlands and river networks mimic warm ocean waters, providing a continuous supply of latent heat. Evaporation from the wet soil will keep the storm artificially energized, slowing down its rate of weakening and extending the period of destructive winds and severe flooding well into October 28 and 29.

Districts in Andhra Pradesh Most Heavily Impacted

Because the storm's most violent wind fields are concentrated in its northern and western sections, 13 to 16 districts have been placed on high alert. The most severe structural wind damage and inundation will hit:

·         Kakinada & Yanam: Sitting directly at the center of the landfall corridor, absorbing the absolute brunt of the 125 kmph landfall winds and severe storm surge.

·         Dr. B.R. Ambedkar Konaseema & East Godavari: Located immediately adjacent to the delta mouth, bearing the core winds and extensive river system flooding.

·         Visakhapatnam & Anakapalli: Positioned in the storm's dangerous northern semicircle, facing continuous gale-force winds up to 100–110 kmph and heavy rain bands spinning directly off the Bay.

·         Eluru & West Godavari: Positioned slightly inland along the western trajectory, receiving forceful winds as the system makes its slow, moisture-fed entry.

Also Read: EXCLUSIVE | Bigger Than Titli, Double of Dana: Cyclone Arnab Landfall Near Kakinada; To Hit Odisha’s Malkangiri on Oct 28 Evening –Districts on Fire Line Inside