An upper-level high pressure system was present at the beginning of the USDM week on Aug. 7, leaving the USVI mostly dry. A weak surface trough moved into the area overnight on Aug. 7 followed by a tropical wave late on Aug. 8 and into Aug. 9, both of which increased moisture, instability, and shower activity. A drier air mass took over briefly on Aug. 11 before another tropical wave passed through the region on Aug. 12, again causing an increase in shower activity. Weather stations throughout the USVI picked up anywhere between 0.08 and 1.00 inch of rain over the course of the week.
On St. Croix, Rohlsen Airport saw 0.08 inch of rain this week. With the rain last week, the August total is already at 1.79 inches or 174% of the normal to date. The year-to-date total of 14.54 inches is 83% of normal. Christiansted Fort saw 0.94 inch of rain this week and sits at 194% of normal for August to date and 80% of normal for the year to date. SPI values for St. Croix on the one-, three-, and six-month scales (ranging from -0.38 to 1.62) indicate drought-free conditions, while values indicate abnormally dry (D0) conditions on the nine-month scale (-0.62), and moderate drought (D1) conditions on the 12-month scale (-0.96). With the continued rain showers this week and improvement in 9-month SPI, St. Croix was improved one category to abnormal dryness (D0-L), with the “L” denoting drier conditions on long-term scales.
St. Thomas’s King Airport recorded 0.28 inch of rain this week. This brings the August rainfall total to 1.64 inches or 141% of normal to date. This follows the wettest July on record. The year-to-date precipitation total amounts to 18.28 inches or 103% of normal. SPI values on one-, three-, six-, nine-, and 12-month time scales ranged between 2.1 and -0.49, all of which indicate drought-free conditions. St. Thomas was improved one category to abnormal dryness (D0-L) with lingering impacts from drier conditions on longer-term scales.
East End ended up with 3.72 inches of rain in July, or 122% of normal. The July rainfall brought the year-to-date total to 14.16 inches which is 83% of normal. A volunteer observer at Windswept Beach recorded 3.62 inches of precipitation in July, which was 106% of the long-term July average for that location. At the end of July, the year-to-date rainfall total of 15.50 inches was 76% of the long-term average. With 1 inch of rain this week, Windswept Beach has seen 1.98 inches of rain so far in August. This puts August 2019 on pace to finish close to the August long-term average of 4.65 inches. At the end of July, SPI values at East End indicated drought-free conditions on the one-, three- and 12-month scales (-0.2, -0.09, and -0.27, respectively), abnormal dryness (D0) on the six-month scale (-0.66), and moderate drought (D1) on the nine-month scale (-1.21). Windswept Beach SPI values from July indicate drought-free conditions on the three-, nine-, 12-month scales (0.02, -0.23 and -0.45), abnormally dry conditions (D0) on the one-month scale (-0.62), and moderate drought (D1) conditions on the six-month scale (-0.96) St. John was improved one category to abnormal dryness (D0-L) with the improved short-term SPI values and continued precipitation.