Cyclone Nivar
Very Severe Cyclonic Storm Nivar was a short-lived but intense tropical cyclone that formed from a low-pressure area over the central Bay of Bengal on 23 November 2020, designated as a cyclonic storm later that day by the India Meteorological Department (IMD).[1] It underwent rapid intensification, reaching very severe cyclonic storm status with maximum sustained winds of 120-130 km/h (75-80 mph) and gusts up to 145 km/h before making landfall near Puducherry along the Tamil Nadu coast around 0230 IST on 26 November.[1][2] The system weakened rapidly over land, dissipating by 27 November after moving northwestward into inland Andhra Pradesh.[1] Nivar produced heavy to very heavy rainfall across southeastern India, triggering flash floods and riverine flooding in coastal districts, with accumulations exceeding 200 mm in some areas near the landfall point.[1] Impacts included the partial or full damage to over 2,600 houses and huts, uprooting of thousands of trees, and destruction of crops across approximately 10,000 hectares of farmland in Tamil Nadu alone.[3] In Andhra Pradesh, the cyclone marooned thousands of homes and led to livestock losses numbering in the hundreds.[4] Fatalities were reported at around five, primarily from falling trees, electrocution, and drowning, reflecting the effectiveness of pre-landfall evacuations that displaced over 300,000 residents from vulnerable coastal zones.[5] The IMD's accurate forecasting, including track and intensity predictions, facilitated these preparations, underscoring improvements in cyclone monitoring during the 2020 North Indian Ocean season.[1]
Meteorological History
Genesis and Initial Development
A low-pressure area formed over the Equatorial Indian Ocean and adjoining central parts of the southern Bay of Bengal on 21 November 2020.[6] This system intensified into a well-marked low-pressure area over the southwest and southeast Bay of Bengal on 22 November.[6] On 23 November at 0230 hrs IST, the depression concentrated over the southwest Bay of Bengal, with estimated maximum sustained surface winds of 30-40 km/h.[6] By the evening of the same day, it strengthened into a deep depression, featuring organized convection and a consolidating low-level circulation center.[6] The system was designated as Cyclonic Storm Nivar on 24 November at 0530 hrs IST, marking the onset of its named tropical cyclone phase, with winds reaching 65-75 km/h gusting to 85 km/h.[6] During this initial development, the cyclone tracked west-northwestwards under the influence of a mid-level ridge to its north, aided by favorable sea surface temperatures exceeding 28°C and low vertical wind shear.[6]Intensification and Peak Stage
Following its designation as a depression on November 23, 2020, at 0230 IST, Cyclone Nivar intensified into a deep depression later that evening over the Bay of Bengal.[7] The system continued to strengthen, becoming the cyclonic storm "Nivar" by 0530 IST on November 24.[7] By 2330 IST the same day, it had escalated to a severe cyclonic storm as favorable atmospheric conditions, including warm sea surface temperatures and low wind shear, supported further organization.[7] On November 25, Nivar underwent additional intensification, reaching very severe cyclonic storm status by 1430 IST, with maximum sustained winds of 120 km/h gusting to 135 km/h.[7] This marked the cyclone's peak intensity around 12 UTC that day, equivalent to approximately 70 knots in Joint Typhoon Warning Center assessments, though the India Meteorological Department, as the Regional Specialized Meteorological Center, classifies intensity based on 3-minute averaged winds.[8] [7] The storm's central pressure at peak was estimated at around 980 hPa, reflecting a compact but intense circulation.[8] Unlike some contemporaries, Nivar exhibited steady rather than explosive intensification over its lifecycle.[9]
Landfall and Dissipation
Cyclone Nivar made landfall along the north Tamil Nadu coast near Puducherry in the late evening of November 25, 2020, with the landfall process commencing around 10:30 pm local time.[10] The cyclone's center crossed the coastline close to Marakkanam, between Puducherry and Chennai, at approximately 3:05 am IST on November 26.[11] At the point of landfall, Nivar was a very severe cyclonic storm with maximum sustained winds of 120–130 km/h (75–81 mph).[11][12] Following landfall, the cyclone rapidly weakened due to interaction with land, dropping in intensity from very severe to a severe cyclonic storm as it moved northwards inland over Tamil Nadu.[10] Winds decreased to 85–95 km/h (53–59 mph) within hours of crossing the coast.[11] The system continued to track northwest, further degenerating into a deep depression amid ongoing terrain-induced friction and reduced moisture availability.[13] Nivar fully dissipated over land by November 27, 2020, after traversing interior regions of Tamil Nadu and southern Andhra Pradesh.[14] The rapid post-landfall weakening was consistent with typical behavior for cyclones making landfall on the Indian east coast, where orographic effects and dry air entrainment accelerate decay.[15]Forecasting and Classification
Intensity Estimates and Warnings
The India Meteorological Department (IMD), as the primary forecasting agency for the North Indian Ocean basin, estimated Cyclone Nivar's intensity using satellite-derived Dvorak technique analyses, scatterometer data, and numerical models such as the Statistical Cyclone Intensity Prediction (SCIP) scheme. The system was initially assessed as a depression with maximum sustained winds of 45 km/h on 23 November 2020, intensifying to a cyclonic storm (62–88 km/h) later that day, a severe cyclonic storm (89–117 km/h) on 24 November, and peaking as a very severe cyclonic storm with 120 km/h sustained winds gusting to 135 km/h on 25 November prior to landfall.[6] These estimates reflected rapid intensification observed between 24 and 25 November, with forecasts predicting peak winds of 100–110 km/h gusting to 120 km/h at landfall near Puducherry.[6] The Joint Typhoon Warning Center (JTWC) provided complementary estimates using one-minute sustained wind metrics, designating Nivar as equivalent to a Category 1 tropical cyclone with peak winds around 120–130 km/h shortly before landfall.[2] IMD issued phased warnings beginning with a pre-cyclone watch on 22 November 2020 for the Tamil Nadu, Puducherry, and south Andhra Pradesh coasts, escalating to a cyclone alert on 23 November and full cyclone warnings from 24 November, specifying gale-force winds, storm surges of 1–2 meters, and heavy rainfall.[6] Orange messages (indicating "be prepared") were issued for Tamil Nadu and Puducherry coasts, while red alerts (signaling "take action") targeted heavy rainfall and wind impacts in coastal Andhra Pradesh and northern Tamil Nadu districts.[14] These warnings, disseminated via bulletins, press releases, and coordination with state disaster management authorities, emphasized evacuation from low-lying areas and fisherfolk safety, with regular updates through 26 November as the system weakened post-landfall.[6]Accuracy of Predictions
The India Meteorological Department (IMD), as the designated Regional Specialized Meteorological Centre for the North Indian Ocean, issued forecasts for Cyclone Nivar's track, intensity, and landfall with errors that generally met or exceeded long-period averages (LPA) from 2015-2019, enabling effective preparations. Track forecast errors were 86.1 km at 24 hours, 126.8 km at 48 hours, and 185.0 km at 72 hours, compared to LPA benchmarks of 80.6 km, 125.5 km, and 171.2 km, respectively; skill scores relative to persistence and climatological forecasts reached 61% at 24 hours, 72% at 48 hours, and 79% at 72 hours, indicating substantial improvement over baseline methods.[16][6] Landfall predictions proved particularly precise, with point errors of 25 km at 24 hours, 25 km at 48 hours, and 16 km at 72 hours—significantly below LPA values of 44.7 km, 69.4 km, and 109.3 km—while timing errors were 0.5 hours at 24 hours, 5.0 hours at 48 hours, and 8.5 hours at 72 hours, versus LPA of 3.0, 5.4, and 8.6 hours. Intensity forecasts underestimated peak winds minimally, with absolute errors of 4.3 knots at 24 hours, 6.5 knots at 48 hours, and 10.2 knots at 72 hours, outperforming LPA errors of 8.9, 13.0, and 15.4 knots; root mean square errors were similarly reduced at 5.0, 9.2, and 11.8 knots against LPA of 11.5, 16.7, and 19.2 knots.[16][6]| Forecast Lead Time | Track Error (km) | Track Skill (%) | Landfall Point Error (km) | Intensity Absolute Error (knots) |
|---|---|---|---|---|
| 24 hours | 86.1 | 61 | 25 | 4.3 |
| 48 hours | 126.8 | 72 | 25 | 6.5 |
| 72 hours | 185.0 | 79 | 16 | 10.2 |