Northeast India Keeps an Eye on Rapidly Strengthening Fani

Gathering its forces over the warm waters of the Bay of Bengal—one of the world’s most dangerous areas for storm surge—Cyclone Fani will pose a serious threat to the coast of northeast India by Friday. As of 12Z Tuesday (8 am EDT), the Joint Typhoon Warning System rated Fani as a top-end Category 2 storm, with top 1-minute sustained winds of 110 mph. At 1430Z (10:30 am EDT), the India Meteorological Department classified Fani as an extremely severe cyclonic storm, with 2-minute top winds around 110 mph putting it the Category 3 range. Fani was centered about 700 miles south-southwest of Kolkata, India.

Fani has more than qualified for rapid intensification, which is defined by the NOAA/NWS National Hurricane center as a jump in sustained 1-minute winds of at least 30 knots (35 mph) in a 24-hour period. During the 24 hours from 6Z Tuesday to 6Z Wednesday, Fani’s top winds increased from 50 mph to 105 mph.

Figure 1. Infrared image of Cyclone Fani as of 1600Z (noon EDT) Tuesday, April 30, 2019, overlaid on the observed and predicted track and Saffir-Simpson ratings of the storm, as forecast by the Joint Typhoon Warning Center. Showers and thunderstorms were widespread across southern India well to the west of Fani's core. Image credit: UW-CIMSS.

Forecast for Fani

Conditions remained very supportive for Fani to gain additional strength on Tuesday. Water temperatures across the cyclone’s path will average 30-31°C (86-88°F), and Fani is passing over a region of enhanced oceanic heat content, which is conductive to rapid intensification. Moderate wind shear of 10 – 20 knots should not impede Fani’s development.

Figure 2. Oceanic heat content (OHC) along the path of Tropical Cyclone Fani projected by the Joint Typhoon Warning Center as of 12Z Tuesday, April 29, 2019. OHC values in excess of 100 kilojoules per square centimeter (darker orange colors) are commonly associated with rapid intensification of tropical cyclones. Image credit: NOAA/RAMMB

Fani’s structure on Tuesday included a distinct eye evident on infrared satellite imagery, surrounded by a symmetric core of intense showers and thunderstorms (convection). One interesting feature is a large zone of convection across far south India, a few hundred miles west of Fani’s center. These thunderstorms are more extensive than those of Fani itself, and it’s possible they are being fueled by ingesting large amount of pollution particles from the Indian subcontinent. Such a process could allow the onshore convection well away from Fani to blossom at the expense of the hurricane’s core circulation. Such a process has been implicated in the behavior of several other intense hurricanes, including Katrina, Irene, and Camille, as discussed by Jeff Masters in a 2015 post and a 2016 follow-up.

Potential impacts from Fani

As of Tuesday night local time, Fani was predicted by JTWC and IMD to make landfall in the Indian state of Odisha (formerly Orissa) on Friday afternoon or evening local time. This forecast is supported by high consistency among our top track models, including the GFS and European models. As Fani approaches the Indian coast, its circulation will gradually nudge inland, so some weakening can be expected prior to landfall. JTWC expects Fani to peak as a Category 4 storm, then weaken slightly before landfall, which would most likely result in a Category 3 landfall. IMD is predicting winds at landfall of 175 to 185 kilometers per hour, near the break point between Cat 2 and Cat 3.

As the storm accelerates north-northeast, a broad swath of coastal and near-coastal areas well north of the landfall location can expect very heavy rains and winds of at least tropical storm strength. This may end up including the Kolkata area, which has more than 10 million residents.

A landfall in Odisha state could put the area around the city of Puri (population around 200,000) in the most dangerous storm quadrant for high winds and storm surge. The surge amounts will be mitigated somewhat by Fani’s angle of approach, as it will not be striking the coast at a perpendicular angle, but storm surge could still be highly destructive, especially if it arrives at or near high tide. Tidal cycles will be accentuated by the approach of a new moon on Saturday. IMD is warning of a potential storm surge of 1.5 meters (around 5 feet) in the Ganjam, Khurda, Puri & Jagatsinghpur districts of Odisha state.

Expert divers and doctors have been stationed on Indian Navy ships positioned at Visakhapatnam and Chennai in advance of the storm, officials told the Times of India. According to the Deccan Herald, there are 879 multipurpose shelters in the state of Odisha that can accommodate about one million people during cyclones. All of these shelters have been readied for potential use, officials said.

Torrential rains, perhaps topping 8” in some locations, are likely to be widespread along Fani’s track as the cyclone moves inland and then parallels the coast, moving toward the Kolkata area.

A look at the tropical moisture surging north with severe Cyclone #Fani toward #India & #Bangladesh. Extensive heavy rainfall is expected. https://t.co/SLWm80Rnpz pic.twitter.com/aNLmvd3kVv

— UW-Madison CIMSS (@UWCIMSS) April 30, 2019

An unusual April cyclone threat to eastern India

Tropical cyclones in the Bay of Bengal tend to occur in two annual peaks on either side of the summer monsoon, most commonly forming in mid-to late spring (April-May) and mid- to late autumn (October-November). The most devastating cyclones tend to be in the autumn, though. Fani would be a rare April landfall for the region, as shown below.

In the past (1891-2017) only 14 severe tropical cyclones formed in APRIL over Bay of Bengal Only one storm crossed the Indian main land. Cyclone FANI the second storm forming in April and crossing main land. Last severe cyclone NARGIS in 2008 devastated Myanmar @Indiametdept pic.twitter.com/jSP2rCmN2N

— Madhavan Rajeevan (@rajeevan61) April 30, 2019

The region’s most catastrophic spring cyclone in recent years was Nargis, which struck Myanmar on May 2, 2008, as a Category 4 storm at an unusually low latitude in a region unaccustomed to tropical cyclones. Nargis led to more than 130,000 deaths and caused some $12.9 billion in damage (2008 USD).

A total of six Bay of Bengal tropical cyclones have hit India at hurricane strength since 2000. The deadliest to hit India in the last couple of decades was the 1999 Odisha Cyclone, which struck near the city of Bhubaneswar on October 29, 1999, as a Category 4 storm with 155-mph winds. Arriving at a near-perpendicular angle, the cyclone drove a storm surge of 26 feet (8 meters) onto the coast. The storm then stalled just inland, dumping torrential rains on portions of India already saturated from the landfall of Category 4 Tropical Cyclone 04B just twelve days before. The catastrophe killed 9,658 people and left $2.5 billion in damage (1999 dollars), making it India's most expensive and fourth deadliest tropical cyclone in the past 100 years.

Dr. Jeff Masters contributed to this post.