Concern Regarding Stronger Hurricane(s) Generation In 2021

La Nina Modoki Risk Later This Year
07/11/2021, 8:09 pm EDT
The June 2021 Global Climate Records/Climate Discussion
07/13/2021, 12:38 pm EDT
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The deep tropics of the North Atlantic basin are becoming somewhat warmer than normal. SSTA of >1C is considered a moderate warm anomaly and much of the deep tropics have recently reached that threshold. Robust warm anomalies of >2C rest on the equator. Anomalous warm SSTA in this region are generally well-correlated with increased convection (and tropical cyclone/hurricane risk) especially if the proper atmospheric conditions are present.

Climate Impact Company ALERT: Concern regarding stronger hurricane(s) generation in 2021.

Fig. 1: The NOAA/NHC weekly SSTA analysis across the North Atlantic and the steady impressive warming of the deep tropics.

Fig. 2: The tendency for early season tropical convection in the outer North Atlantic deep tropics persists.

Fig. 3: Multivariate ENSO index (MEI) has stayed in a La Nina mode into middle 2021. The reason is a La Nina-like convection pattern in the tropical Pacific Ocean. However, also note the enhanced convection tendency in tropical West Africa where tropical waves are born that can lead to North Atlantic hurricanes.

Discussion: The deep tropics of the North Atlantic basin are becoming somewhat warmer than normal. SSTA of >1C is considered a moderate warm anomaly and much of the deep tropics have recently reached that threshold (Fig. 1). Robust warm anomalies of >2C rest on the equator. Anomalous warm SSTA in this region are generally well-correlated with increased convection especially if the proper atmospheric conditions are present. Early season anomalous convection has persisted in the central/east deep tropics of the North Atlantic basin from June into July (Fig. 2). Recently, Climate Impact Company issued a statement that despite the oceanic signals identifying an end to La Nina last MAR/APR the multi-variate ENSO index (MEI) has maintained a moderate La Nina climate. The La Nina-like MEI is caused by the convection patterns in the equatorial Pacific which have remained very La Nina-like through quarter 2 of 2021 (Fig. 3). Also note that in tropical West Africa an environment favoring enhanced convections persists. This observation coupled with warming waters of the deep North Atlantic tropics supports increased risk of unusually strong tropical events (hurricanes) emerging in the deep tropics once we’re into the core of the tropical cyclone season. Pay close attention to the climatology deep tropics tracks for tropical cyclones in August and September according to NOAA/NHC (Fig. 4-5). These deep tropics tracks usually produce the strongest hurricanes!

Fig. 4: NOAA/NHC climatology of tropical cyclone tracks in August.

Fig. 5: NOAA/NHC climatology of tropical cyclone tracks in September.