September 2021 Climate Summary for Belize
September in Belize marks the peak of the hurricane seas and the secondary maxima for rainfall over most areas. Apart from tropical systems, rainfall is typically attributed to 6 Upper-Level Troughs, 7 Tropical waves, 3 Surface Troughs, 2 Cold Core Lows and 1 Mid-Upper Level low on average. However, the passage of tropical waves and surface troughs over the area was below average resulting in below normal rainfall over most areas.
The north Atlantic high-pressure ridge prevailed over the area during week 1 supporting a light to moderate easterly surface flow. Only isolated showers and thunderstorms were observed. Conditions became moist and unstable between September 3 to 7 due to a surface trough over the area and an upper level TUTT extending into the Gulf of Honduras that lingered throughout the week. Moist conditions extending through to the upper levels and the TUTT supported divergent conditions over Belize. This led to an increase in shower and thunderstorms activity across the country, especially over northern and central locations. The wettest days during this week were September 3 and 4 as the TUTT low became stationary over Belize fuelling rainfall and thunderstorm activity.
Week 2 continued moist through to the upper levels and unstable as a tropical wave approached the area. This wave crossed the country on September 9 brining with is a few showers and thunderstorms which started over the northern parts of the country and increased during the night. Most of the rainfall activity was behind this wave with showers and thunderstorms increasing and spreading over most areas on September 10, especially over central and southern locations. The surface winds during this period were predominately easterly and became north-easterly with the passage of the wave. At the upper levels, a ridge TUTT pattern prevailed with a west to north-westerly component and neutral to weakly divergent conditions. Moisture levels began to decrease after September 11 as the ridge pattern returned with a tight pressure gradient supporting moderate to occasionally gusty east to north-easterly winds. Another tropical wave approached the country on September 13, but no significant showery activity was associated with it due to dry lower and upper-level conditions and a neutral to weakly convergent pattern hence only isolated showers and thunderstorms were observed, mostly over southern locations.
A light east to east to south-easterly airflow prevailed into week 3 as the high-pressure ridge was the dominant feature influencing our weather from September 15 to 21. The surface winds became east north-east towards the end of the week. Most of the moisture was capped below 850 hPa while the upper levels continued dry. Mainly fair weather with overnight showers or isolated thunderstorms occurred over northern, coastal, and southern portions of the country. On September 18, a tropical wave coupled with an inverted trough at the upper levels crossed the country with a few showers and isolated thunderstorms affecting the south and mountainous areas. Tropical Depression Peter was to the northeast of Puerto Rico and Tropical Storm Rose was to the northwest of Cabo Verde Islands on September 21 but none of these systems posed a threat to Belize. The upper-level ridge supported an east to north-easterly flow and the TUTT which has become zonal persisted in the area.
Conditions became moister and more unstable during the last week of the month as moisture convergence occurred over the area due to an early season cold front over the Bay of Campeche. Winds were light and an east to north-easterly surface flow prevailed. At the upper levels, the nigh centre over the area supported a north to north-westerly flow along with a neutral to divergent pattern. Some showers, periods of rain and thunderstorms affected moistly southern, coastal, and offshore areas until September 27. Thereafter, moisture levels decreased in both the low and upper levels and the upper-level pattern became convergent at the end of the month. Mainly fair weather closed out the month with isolated showers and thunderstorms over the south and along the western border of September 30. At the end of this month, Hurricane Sam and Tropical Storm Victor were located to the northeast of the Lesser Islands and south of the Cabo Verde islands, respectively.