Scattered moderate rains affected the Commonwealth last week, perpetuating the trend in recent weeks for improvement to outpace deterioration. Dryness eased its grip on some areas in the north-central, eastern, and southwestern Puerto Rico while other locations were not significantly different than one week prior.
Early in the drought week (Wed, Sep 30 – Tue, Oct 6, 2026), synoptic drivers for the weather conditions observed across the islands included an upper-level low pressure system positioned northeast of the USVI with upper-level convergence across the forecast area, inhibiting the development of deep thunderstorm activity. By mid-period, showers were noted to pass over the islands with the main trough now west of the area over Hispaniola. Conditions aloft over the USVI gradually became less favorable for strong convection as temperatures warmed and mid-level lapse rates weakened. The heat threat was more prominent towards the end of the drought week, along with an increased risk of afternoon thunderstorms.
Weekly estimated rainfall amounts from satellite-based NASA SPoRT (GPM IMERG) data ending Oct 6th at 1200 UTC ranged from near zero to about 0.8-inch, with somewhat higher amounts indicated over Puerto Rico (several inches), especially the western portion of the Commonwealth.
At St. Croix, precipitation amounts in descending order included: VI-SC-35 (Frederiksted 1.3 ENE, 1.66 inches, 6 days of data), VI-SC-20 (Frederiksted 1.7 ESE, 0.66-inch), VI-SC-10 (Christiansted 1.6 E, 0.39-inch), VI-SC-23 (Christiansted 6.5 W, 0.38-inch, 5 days), VI-SC-29 (Frederiksted 2.5 NNE, 0.37-inch), VI-SC-37 (Frederiksted 5.6 E, 0.30-inch, 5 days), VI-SC-32 (Frederiksted 1.9 NNW, 0.30-inch, 3 days), VI-SC-30 (Christiansted 1.7 SW, 0.25-inch), VI-SC-25 (Christiansted 4.4 W, 0.14-inch), and VI-SC-24 (Christiansted 2.1 ENE, 0.04-inch, 1 day). The Adventure 28 Well water level varied between 26.30 feet and 26.64 feet below the land surface during this period. At East Hill (#672560) the Standardized Precipitation Index (SPI) at 1, 3, 6, 9, and 12-months were, respectively: -1.67, -2.22, -2.35, -1.3, and -1.7. This is consistent with D3/D4 conditions and if next week continues to be abnormally dry, St. Croix’s drought depiction may be degraded further to D4.
Rainfall totals at St. John ranged from 0.62-inch at VI-SJ-5 (Cruz Bay 1.6 E) to 0.02-inch at VI-SJ-10 (Cruz Bay 3.1 NNW). Intermediate amounts included 0.05-inch at VI-SJ-11 (Coral Bay 0.7 NW, 4 days of data), 0.10-inch at VI-SJ-8 (Cruz Bay 7.4 E, 2 days of data), and 0.15-inch of rain at VI-SJ-3 (Windswept Beach). In addition, Windswept Beach reported a total of only 2.63 inches of precipitation for the entire month of September. The drought has stretched out to 5 months now, from May through September 2026. Each of those 5 months has featured a rainfall deficit (compared to the 1984-2025 mean value) greater than 2 inches, which totals 13.22 inches. The well-water level at the Susannaberg Dpw 3 Well showed a steady decline throughout the period, from 19.11 feet below the land surface at the start to 19.35 feet at the end of the period. The SPI values at Windswept Beach (VI-SJ-3) at (1, 3, 6, 9, and 12-months) are, respectively: -2.26, -1.72, -2.17, -1.22, and -1.76. These values are comparable to those at the shorter 1- and 3-month periods for St. Croix, and if deterioration continues next week, St. John’s drought depiction will also be degraded from D3-S to D4-S.
At St. Thomas, an even half-inch of rain was reported at VI-ST-5 (Charlotte Amalie West 4.2 WNW) and 0.41-inch at VI-ST-15 (Charlotte Amalie West 1.3 N). The groundwater level at the Grade School 3 Well began the period at 9.26 feet below the land surface, and finished at 8.98 feet near the very end of the period. It appears that some rain fell on Oct 3 (assuming no human water management was involved), boosting the well water level to 9.06 feet by the middle of that afternoon. The water level gradually declined thereafter until the late evening of Oct 6, when another shower boosted the well level to 8.98 feet. This week, St. Thomas retains its D4-S designation.
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