METEOROLOGICAL SERVICE JAMAICA CLIMATE BRANCH PRELIMINARY MONTHLY RAINFALL SUMMARY FOR MARCH 2016 Introduction This rainfall summary is prepared by the Climate Branch of the Meteorological Service, Jamaica. The Meteorological Service maintains a network of over two hundred (200) rainfall stations located across the island. Rainfall is usually read at 7am by a cadre of paid but mainly voluntary dedicated observers and reported for the previous 24 hours. General Jamaica s bimodal rainfall pattern consists of two peak periods with higher values of rainfall and corresponding periods of lower rainfall amounts. 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 and deviations from this pattern do occur year to year. A comparison of the old 30 year mean (1951-80) with the 1971-2000 mean by the Meteorological Service has shown that the island s rainfall patterns and values have not changed significantly for the current thirty-year (1971-2000) period. The main changes noted are that of wetter dry periods and drier wet periods. This has however not affected the overall rainfall pattern for the island. Figure 1: Precipitation Pattern for 1971-2000 for the island of Jamaica.
Climate Branch March 2016 2 Island Monthly Rainfall March 2016 had all thirteen (13) parishes recording below normal rainfall. Overall the island s average rainfall was 41mm which corresponds to 47% of the 30-year (1971-2000) mean. These values were well below those of March 2015 which had 108mm or 123% respectively. The cumulative rainfall for the island to date (March 2016) was 258mm, or 91% of the 30-year (1971-2000) mean or 9% below what is normal for this time of the year. Parish Mean Rainfall for March 2016 (Rainfall in mm) MAR MAR MAR % OF 30 YR NORMAL 2016 2015 30 YR NORMAL (1971-2000) 2016 2016 2016 JAN FEB MAR Parishes KEY Hanover HAN 64 169 104 56 180 62 Westmoreland WES 33 96 88 87 122 38 Manchester MAN 40 124 91 57 73 44 St. Elizabeth STE 51 95 99 61 78 52 Clarendon CLA 39 18 56 21 81 69 St. Catherine STC 20 36 61 64 192 32 Trelawny TRE 12 76 61 147 213 19 St. James STJ 23 94 60 102 391 38 St. Ann STA 36 131 71 94 264 51 St. Mary STM 42 178 108 61 186 39 Portland POR 126 303 209 48 137 60 St. Thomas STT 17 42 68 40 89 24 Kgn. & St. And. KSA 34 49 67 33 140 51 Jamaica JAM 41 108 88 65 162 47 Table 1: Parish Mean Rainfall for March 2016 (Rainfall in mm) 2
Climate Branch March 2016 3 Assessment of Parish Figures All parishes recorded rainfall totals that were below their 30-year means. The parish rainfall figures indicate the following: Clarendon with the highest of 39mm or 69%, followed by Hanover with 64mm or 62%, Portland with 126mm or 60%, St. Elizabeth with 51m or 52%, KSA with 34mm or 51%, St. Ann with 36mm or 51%, Manchester with 40mm or 44%, St. Mary with 42mm or 39%, St. James with 23mm or 38%, Westmoreland with 33mm or 38%, St. Catherine with 20mm or 32%, St. Thomas with 17mm or 24% and Trelawny with 12mm or 19%. (Kindly note that Kingston and St. Andrew (KSA) are combined and reported as one. Drought Conditions Definition 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 stream-flow 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. Methodology and Index Locally, the onset and the duration of a meteorological drought is determined by comparing the average rainfall over a period of two consecutive months with the 30-year historical averages (normal) for a similar bi-monthly period for each parish and the 3
Climate Branch March 2016 4 island. The percentage value that is generated is used to quantify the thresholds of the drought index that is presented in Table 2. This index is similar to that used by the Australian Meteorological Service except for the duration of eight consecutive weeks instead of bi-monthly periods that is used locally. Percentage of Normal for 2 Drought Condition or Status Consecutive Months 20% or less Extreme Drought 21% to 40% Severe Drought 41% to 60% Normal Drought Above 60% No Drought Table 2: Meteorological Drought Index Drought Indices (%) for December 2015 to March 2016 Parishes Dec/Jan Jan/Feb Feb/Mar Hanover 89 123 123 Westmoreland 79 105 78 Manchester 69 65 56 St. Elizabeth 72 70 63 Clarendon 138 50 74 St. Catherine 64 129 109 Trelawny 102 179 131 St. James 102 237 213 St. Ann 63 169 165 St. Mary 53 115 121 Portland 119 87 103 St. Thomas 112 62 59 Kgn. & St. And. 48 87 97 Jamaica 89 111 106 Table 3: Drought indices (%) for December 2015 to March 2016 Table 3 is calculated as follows: Values = {(Month 1 + Month 2) / (Normal month 1 + Normal month 2)} x 100 Drought Assessment Manchester and St. Thomas were the parishes to record (normal) drought conditions this bi-monthly period. Clarendon which recorded drought conditions the previous period was 4
Climate Branch March 2016 5 above drought conditions this time around. All other parishes remained above drought conditions. FORECAST Precipitation Outlook for the period April to June 2016 Through the period April to June the models continue to indicate an increase in the forecast rainfall amounts across most areas. As we approach the first rainfall season (April-June), the expected increase in rainfall activities is likely to ease most of the current dry patches affecting sections of most southern parishes. The forecast is for the rains to start very late April into May, and therefore the timely arrival of these rains should ease the water stress currently affecting key agricultural areas. However due to the variability in the start date of the rains, we would advise that monitoring activities be continued to reduce any possible impacts that could result should there be any delays in the start of the rains. VERIFICATION OF MODELS For the same period last year, the models predicted near normal to above normal rainfall for most sections of the island. A comparison with actual conditions indicates that most parishes recorded below normal (less than what is expected) or near normal (expected) rainfall for the three-month period April to June. Although forecast confidence can be low at this time of the year, we remain very optimistic that there is a strong realization of the forecast going into the first rainfall season, (April-June). 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 5
Climate Branch March 2016 6 Table 4. Climate Predictability Tool (CPT) Station Outlook- AMJ Stations Below (B) % Normal (N) % Above (A) % Manley (Kingston) Sangster (St. James) Savanna La Mar (Westmoreland) Beckford Kraal (Clarendon) Serge Island (St. Thomas) Cave Valley (St. Ann) Tulloch Estate (St. Catherine) Y.S. Estate (St. Elizabeth) Hampstead (St. Mary) Orange Valley (Trelawny) 25 35 40 Langley (Kingston) 25 35 40 Mount Peto (Hanover) Shirley Castle (Portland) Suttons (Manchester) Potsdam (St. Elizabeth) Frome (Westmoreland) Worthy Park (St. Catherine) 25 35 40 30 30 40 Jamaica 6
Climate Branch March 2016 7 Summary All parishes reported below-normal rainfall for the month of March 2016, with Jamaica receiving only 47% of its normal rainfall. Two parishes experienced drought conditions, while the other eleven parishes remained above drought. The current projections still indicate an increase (near to above normal) in rainfall from April to June, and it is expected that the rains should ease the dry conditions affecting sections of the island. 7