August Figure 1: Precipitation Pattern from for Jamaica.

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1 August 2018 Introduction This rainfall summary is prepared by the Climate Branch of the Meteorological Service, Jamaica (MSJ). The MSJ maintains a network of rainfall stations located in every parish across the island. Rainfall is usually read at 7:00 a.m. and reported for the previous 24 hours. These readings are done by a cadre of paid but mainly voluntary dedicated observers. that of wetter dry periods and drier wet periods. This has however not affected the overall rainfall pattern for the island as seen in Figure 1 below. General Jamaica s bimodal rainfall pattern consists of two peak periods with higher values of rainfall and corresponding periods of lower rainfall. The primary peak occurs in October and the secondary in May. The lowest amounts are at a minimum during the period February to March and the month of July. This is based on long-term reports but deviations from this pattern do occur year to year. Figure 1: Precipitation Pattern from for Jamaica. A comparison of the old 30-year mean ( ) with the mean by the MSJ has shown that the island s rainfall patterns and values have not changed significantly for the current thirty-year ( ) period. The main changes noted are Prepared by the Climate Branch Meteorological Service, Jamaica 65 ¾ Half Way Tree Road Kingston 10 Telephone: (876) / datarequest@metservice.gov.jm

2 HIGHLIGHTS FOR AUGUST Ten of thirteen parishes received below-normal rainfall. Six (6) of thirteen (13) parishes recorded meteorological drought. Near-normal rainfall is forecast for the island, for September to November. Near-normal temperatures are forecast for the next 3 months Parish Mean Rainfall and Comparison with 30-yr Averages AUG AUG AUG % OF 30 YR NORMAL 30 YR NORMAL ( ) Parishes KEY JUN JUL AUG Hanover HAN Westmoreland WES Manchester MAN St. Elizabeth STE Clarendon CLA St. Catherine STC Trelawny TRE St. James STJ St. Ann STA St. Mary STM Portland POR St. Thomas STT Kgn. & St. And. KSA Jamaica JAM Table 1: Parish Mean Rainfall and Comparison with 30-yr Averages 2

3 Rainfall Assessment For August 2018, ten (10) of thirteen (13) parishes 1 recorded below-normal rainfall. These ten parishes also received less rainfall in August 2018 when compared to August Two parishes namely, Westmoreland and St. Catherine, recorded above-normal rainfall in August 2018, as well as, received more rainfall for the month, when compared to one year ago. Trelawny also recorded above-normal rainfall in August 2018, but, received less rainfall when compared to one year ago. The percentages of mean rainfall in August were lower for 8 parishes when compared to those of July and higher for the other 5 parishes. Overall, the island s average rainfall for August was 111 mm, which is 19 mm less than that received one year ago, and which corresponds to 65% of the 30-year ( ) monthly mean value. The island generally, as well as, two (2) parishes namely, Hanover and St. Elizabeth recorded 3 consecutive months of increasing rainfall percentages. No parish recorded decreasing rainfall percentages, throughout the same period. There were five (5) parishes, namely, St. James, Clarendon, Kingston & St. Andrew, St. Thomas and St. Mary that received 50% or less of their 30-year monthly mean rainfall in August. In addition, Clarendon, Kingston & St. Andrew and St. Mary were doing so for 3 consecutive months. The five parishes that received more than 50% but less than 100% of their normal rainfall for the month were, Hanover, St. Elizabeth, Manchester, Portland and St. Ann. The parishes receiving more than 100% of their mean monthly rainfall were Westmoreland, St. Catherine and Trelawny. Across the island, the parish percentages of the 30-year monthly means ranged from 19% for St. Mary to 131% for St. Catherine. 1 Note that Kingston and St. Andrew (KSA) are combined and reported as one parish. 3

4 Fig.2. Distribution of Jamaica s Rainfall for August 2018 Fig.3. Thirty-year ( ) Mean Island Rainfall for August Drought Conditions Meteorological Drought Methodology and Index The Standardized Precipitation Index (SPI), developed by T.B. McNee, N.J. Doesken, and J. Kleist in 1993, is a tool used to monitor drought conditions based on precipitation. The SPI can be used to monitor conditions on a variety of time scales ranging from 1-month to 12-months. This temporal flexibility allows the SPI to be useful in both short-term meteorological, agricultural and long-term hydrological applications by providing early warning of drought and for making assessments on the severity of a drought. The MSJ calculates an observed SPI (see Table 2) using a 2-month time interval. Drought is defined as a long period of weather without rain (Heinemann English Dictionary). The more precise definitions for specific areas of concern that are most commonly used are: Agricultural drought a period when soil moisture is inadequate to meet the demands for crops to initiate and sustain plant growth. Hydrological drought period of below average or normal streamflow and/or depleted reservoir storage. Meteorological drought a period of well-below average or normal precipitation (rainfall) that spans from a few months to a few years. 4

5 Parish Drought Assessment Observed SPI for May to August 2018 Parishes May/Jun Jun/Jul Jul/Aug Hanover Westmoreland Manchester St. Elizabeth Clarendon St. Catherine Trelawny St. James St. Ann St. Mary Portland St. Thomas Kingston & St. Andrew Table 2: Parish SPI for May to August 2018 SPI Value Category SPI Value Category 0.00 to Near Normal 0.00 to 0.50 Near Normal to Abnormally Dry 0.51 to 0.79 Abnormally Wet to Moderately Dry 0.80 to 1.29 Moderately Wet to Severely Dry 1.30 to 1.59 Severely Wet to Extremely Dry 1.60 to 1.99 Extremely Wet or less Exceptionally Dry 2.00 or more Exceptionally Wet Table 3: Severity Classes of the SPI Drought Index Discussion Based on the latest SPI figures for July/August, 4 parishes (St Elizabeth, St James, St Thomas, and Kingston & St. Andrew) have shown consecutive decreases (deterioration/drier conditions) in their SPI values over the last 3 bi-monthly periods. For July/Aug, there were ten (10) parishes recording SPI values of lower than -0.90, which equates to rankings ranging from moderately dry to extremely dry conditions. There were 6 parishes namely, St. Elizabeth, Clarendon, Kingston & St. Andrew, St. Thomas, St. Mary and St. James that recorded meteorological drought conditions in the July/August period. 5

6 Westmoreland and St. Catherine have recorded large increases (ie. >0.70) in their SPI values over the last 2 bi-monthly periods, with the rankings for both parishes moving from moderately dry to near-normal (dry) conditions. The following 4 parishes recorded moderately dry conditions namely, Manchester, Kingston & St. Andrew, Portland and St. Ann. Five other parishes had rankings of severely dry namely, St. Elizabeth, Clarendon, St. Thomas, St. Mary and Hanover. For a 3 rd consecutive bi-monthly period, St. James had the lowest SPI value. The ranking for Jul/Aug was extremely dry. Meanwhile, Trelawny had the highest SPI value (-0.02) with a ranking of near-normal (dry). See Fig 4 below for the current drought conditions. Fig.4. Drought Analysis for July-August 2018 Precipitation and Temperature Outlook: September to November 2018 During the next three months which includes the traditional primary wet season, the forecast models are indicating that Jamaica should receive near-normal rainfall. Should this forecast materialize, it could reverse some of the deficits in rainfall that had occurred since June and, therefore, bring some relief from the existing dry/drought conditions across the island. Nearnormal temperatures are also still expected across the island over the same period. Table 4 below, shows the Precipitation Outlook for 17 selected stations across Jamaica as analysed by the Climate Predictability Tool. For the September to November 2018 period, three of seventeen stations are indicating higher probabilities for below-normal rainfall. Another ten 6

7 stations are indicating higher probabilities for normal rainfall while, the remaining four stations are indicating higher probabilities for above-normal rainfall. Stations Parishes Below (B) % Normal (N) % Above (A)% Beckford Kraal Clarendon Mount Peto Hanover Manley Airport Kingston Lawrence Tavern Kingston Suttons Manchester Shirley Castle Portland Cave Valley St. Ann Tulloch Estate St. Catherine Worthy Park St. Catherine Y.S. Estate St. Elizabeth Potsdam St. Elizabeth Sangster St. James Serge Island St. Thomas Hampstead St. Mary Orange Valley Trelawny Savanna-La-Mar Westmoreland Frome Westmoreland Key A: Above-normal rainfall means greater than 66 percentile of the rank data N: Near-normal rainfall means between 33 and 66 percentile of the rank data B: Below-normal rainfall means below 33 percentile of the rank data Table 4: Precipitation Outlook for Selected Stations for September to November 2018 Forecast Verification For the same period last year, September-November 2017, the models performed generally well, with accuracy in the range of percentage points. The initial forecast indicated that rainfall was likely to be near-normal to above-normal for the period. Preliminary findings indicated that most stations recorded near-normal to above-normal rainfall amounts during the period. 7

8 Summary Ten of thirteen parishes recorded rainfall amounts that were below their respective 30-year ( ) monthly means. Overall, Jamaica recorded rainfall of 65% of its normal rainfall in August. On the parish level and for a third consecutive month, Clarendon, Kingston & St. Andrew and St. Mary, were the parishes to receive 50% or less of their normal monthly rainfall amounts. St. James and St. Thomas also received less than 50% of their 30-year August rainfall. Hanover, St. Elizabeth, Manchester, Portland and St. Ann were the parishes that received more than 50% but, less than 100% of their 30-year monthly means. Westmoreland, St. Catherine and Trelawny were the parishes receiving more than 100% of their mean monthly rainfall. St. Elizabeth, Clarendon, Kingston & St. Andrew, St. Thomas, St. Mary and St. James were the parishes that recorded meteorological drought conditions in the July/August bi-monthly period. The projection over the traditional primary rainfall season (September to November) is for nearnormal rainfall across the island. Should this forecast materialize, it would reverse the deficits in rainfall that have been experienced since June and therefore, bring some relief from the existing dry/drought conditions across the island. 8