India Meteorological Department

The India Meteorological Department has issued yellow alerts for several Kerala districts as the El Niño phenomenon begins to weaken the current monsoon season. While overall rainfall intensity is expected to decrease, officials warn of sudden extreme downpours and strong winds, with some areas facing immediate orange alerts.

Conflicting Reports on Yellow Alert Districts

Meteorological reports for the current period show significant discrepancies regarding which specific districts are under yellow alerts. Manorama Online identifies five districts—Pathanamthitta, Kottayam, Idukki, Ernakulam, and Kasaragod—as being under yellow alert today. However, News18 Malayalam reports that only four districts, specifically Pathanamthitta, Kottayam, Idukki, and Ernakulam, are under the warning.

The situation in Ernakulam is particularly volatile. The agency has issued a localized orange alert for Ernakulam that is expected to last for only three hours, warning of moderate rain accompanied by wind speeds reaching 40 kilometers per hour.

Looking toward the immediate future, Indian Express reports that Kottayam and Ernakulam will face yellow alerts again tomorrow, June 16. Meanwhile, a different set of warnings has been issued for northern regions, with reports from manoramanews.com noting yellow alerts specifically for Kozhikode, Kannur, and Kasaragod.

El Niño and the Projected Decrease in Rainfall

The broader monsoon pattern is undergoing a shift due to atmospheric changes in the Pacific Ocean. The Central Meteorological Department indicates that the El Niño phenomenon is currently active in the equatorial regions of the Pacific, which is expected to weaken the monsoon’s overall strength across Kerala.

This phenomenon is characterized by the warming of sea surface temperatures in the central and eastern equatorial Pacific. Such warming can disrupt the Walker Circulation, a large-scale atmospheric movement that plays a critical role in global weather patterns. For the Indian subcontinent, this disruption can alter the pressure gradients that drive the monsoon, potentially reducing the moisture transport necessary for sustained rainfall.

This phenomenon has already begun to influence sea surface temperatures. In the months of April, May, and June, the average temperature deviation exceeded the El Niño threshold of 0.5 degrees Celsius. While this typically results in below-average seasonal rainfall, officials warn that the reduction in intensity does not eliminate the risk of danger.

The Monsoon Mission Coupled Forecast System suggests that the Indian Ocean Dipole is currently in a neutral state. This neutral condition is expected to persist until the end of the monsoon season. Despite the overall trend of declining rain, forecasters have issued a specific caution: the public must remain vigilant against sudden, extremely heavy rainfall episodes that can occur even as the season weakens.

Understanding the IMD Alert System

The India Meteorological Department utilizes a color-coded warning system to communicate weather risks to the public and local government agencies. This hierarchy is designed to provide scalable responses to varying levels of intensity. A “Yellow Alert” serves as a warning to be aware of potential weather hazards, indicating that weather conditions could become significant. An “Orange Alert” represents a higher level of caution, signaling that the weather may become severe and that residents should be prepared for potential disruptions. This tiered system allows disaster management authorities to mobilize resources and for citizens to take precautionary measures before extreme events occur.

Yellow alert in 12 districts in #kerala

Maritime Risks and Wind Speed Forecasts

Wind conditions and sea safety present a complex picture for coastal residents and fishermen. Wind speeds are expected to fluctuate between 30 and 40 kilometers per hour in various parts of the state, with higher gusts possible in specific corridors.

Weather models provide the following wind and rain projections:

Heavy Rainfall Threshold: 64.5 mm to 115.5 mm within a 24-hour period.
Somalian and Arabian Sea Winds: 45 to 55 km/h, potentially reaching 65 km/h.
Tamil Nadu and Gulf of Mannar Winds: 40 to 50 km/h, with occasional gusts of 60 km/h.

For Kerala’s coastal communities, these meteorological shifts have direct economic and safety implications. The fishing industry relies heavily on accurate wind and sea-state forecasts to manage daily operations. When wind speeds reach the thresholds mentioned, such as the 45 to 65 km/h gusts predicted in the Somalian and Arabian Sea corridors, the risk of maritime accidents increases significantly. Consequently, fishing prohibitions are a standard safety measure used to protect lives at sea during periods of high-energy sea states.

There are also conflicting reports regarding maritime activity. While some updates suggest that fishing remains unobstructed along the Kerala, Karnataka, and Lakshadweep coasts today, other reports indicate that fishing has been strictly prohibited along the Kerala coast due to rough sea conditions.

Rainfall Thresholds and Localized Conditions

To clarify the meteorological terminology being used, officials define “heavy rain” in this context as precipitation falling between 64.5 millimeters and 115.5 millimeters over a 24-hour window. This threshold is the primary driver behind the current yellow alerts.

By distinguishing between “heavy” and “very heavy” rainfall using these specific millimeter thresholds, meteorological services provide a standardized metric for predicting potential flooding. In high-altitude or hilly regions, these specific precipitation levels are closely monitored because they can trigger rapid changes in soil stability and river levels.

Recent localized weather has already shown signs of volatility. Thiruvananthapuram, for instance, experienced continuous heavy rainfall throughout the previous night. While the immediate trend suggests a decrease in monsoon strength, meteorological experts suggest that precipitation levels may experience another surge by the end of next week.

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How humidity drives the heat index

The heat index measures how hot it feels when relative humidity is combined with the air temperature. While the thermometer may read 43.5°C, the presence of water vapor in the atmosphere dictates the actual thermal stress experienced by the human body.

When humidity levels rise, the air becomes more saturated with moisture. This saturation reduces the rate at which liquid water can transition into a gaseous state. This vapor pressure gradient refers to the difference in moisture concentration between the skin and the surrounding air. When the air is already near its saturation point, the gradient is minimal, meaning there is little capacity for the air to accept additional moisture from the skin.

Because the body relies on the evaporation of sweat to release heat, a high-humidity environment effectively traps heat against the skin. The India Meteorological Department (IMD) uses these combined metrics to issue heatwave warnings, as the perceived temperature often exceeds the actual ambient temperature by several degrees.

The science of evaporative cooling and thermoregulation

Human thermoregulation depends heavily on latent heat of vaporization. As sweat evaporates from the skin, it absorbs thermal energy from the body, providing a cooling effect. In dry conditions, this process is efficient. However, when the air is already laden with moisture, the vapor pressure gradient between the skin and the atmosphere decreases.

As this gradient narrows, sweat stays on the skin rather than evaporating. This failure in the cooling mechanism causes the body’s core temperature to rise more rapidly. At an ambient temperature of 43.5°C, the body is already struggling to shed heat through convection because the surrounding air is nearly as warm as the body itself. Without effective evaporation, the risk of heat exhaustion increases.

To assist in this process, the body employs vasodilation. During vasodilation, blood vessels near the skin’s surface widen, allowing more blood to flow to the periphery to facilitate heat transfer from the core to the skin. This process, however, places an increased demand on the cardiovascular system, as the heart must work harder to maintain blood pressure while circulating blood to the skin’s surface.

Urban heat islands and radiant heat absorption

The physical environment in Delhi contributes to higher perceived temperatures through the urban heat island effect. Urban materials, such as concrete, asphalt, and brick, possess high thermal mass. These surfaces absorb solar radiation throughout the day and re-emit it as long-wave infrared radiation.

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This absorption is heavily influenced by the albedo of urban surfaces—the measure of how much solar radiation a surface reflects. Darker materials like asphalt have low albedo, absorbing the majority of solar energy, whereas lighter surfaces or natural vegetation have higher albedo and reflect more heat. Additionally, the verticality of modern urban architecture can create “urban canyons,” where tall buildings restrict wind flow and trap heat between structures, preventing the natural convection that would otherwise help cool the environment.

This radiant heat adds a secondary layer of thermal stress. Even if a person is in the shade, they may still receive significant heat from the surrounding buildings and roads. This constant re-emission of energy prevents the local environment from cooling down effectively, even after the sun has begun to set. The combination of high ambient air temperature, moisture-driven heat index increases, and radiant heat from infrastructure creates a multi-layered thermal load.

Health implications of high apparent temperatures

Medical authorities monitor the heat index because it is a more accurate predictor of heat-related illnesses than air temperature alone. Occupational exposure is a significant factor in heat-related morbidity; individuals engaged in outdoor labor, such as construction workers and street vendors, face higher risks due to prolonged sun exposure and physical exertion. Maintaining electrolyte balance is also critical, as the loss of water through sweat also depletes essential salts like sodium and potassium.

Heat exhaustion: Characterized by heavy sweating, rapid pulse, and dizziness, occurring when the body loses excessive fluids and electrolytes.

Heatstroke: A critical condition where the body’s thermoregulatory system fails entirely, causing the core temperature to rise above 40°C.

The IMD and health officials suggest that during periods where the heat index is significantly higher than the recorded 43.5°C, the risk of cardiovascular strain increases, particularly for vulnerable populations such as the elderly and those with pre-existing respiratory conditions.

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