Tropical Upper Troposphere Trough Continues to Protect Western North Atlantic Basin from Tropical Activity

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Highlight: Tropical upper troposphere trough protects western North Atlantic basin from tropical activity. Feature likely to last into final third of August.

Fig. 1: A tropical upper tropospheric trough is identified over the Caribbean Islands in the morning 250 MB (high-level) wind analysis.

Discussion: Inhibiting tropical cyclone development across the western half of the North Atlantic basin in July and into August is evolution of a tropical upper tropospheric trough (TUTT). In the upper troposphere, on average, wind direction is out of the north across the Gulf of Mexico and becomes westerly in the Caribbean Sea and then northerly over Puerto Rico on the back side of an upper-level ridge pattern in the southeast North Atlantic (Fig. 1). So far in August, an upper trough is apparent at 250 MB centered over Southern Florida/Western Cuba also identifying presence of TUTT (Fig. 2). The TUTT pattern remains over the next 2 weeks. In 15 days, ECM ENS indicates TUTT is weaker but still present across the Caribbean Sea (Fig. 3). The TUTT pattern strongly inhibits tropical cyclone development through the middle third of August. The TUTT pattern is likely to ease later this month. Implications are that an active hurricane season ahead forecast is delayed and either less active than forecast or very active over a relatively short period of time. The last time TUTT was present during early August was in 2013. In 2013, 10 of 14 tropical cyclones occurred after mid-August and only 2 hurricanes formed. The season lasted into early December.

Fig. 2: The early August 250 MB anomaly analysis identifies presence of a tropical upper tropospheric trough.

Fig. 3: The ECM ENS 250 MB wind forecast in 15 days identifies presence of the TUTT remaining over the northern Caribbean Sea although weaker.