March 2019

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.

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 of 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.

A comparison of the old 30-year mean (1951-1980)

with the 1971-2000 mean by the MSJ 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 as seen in Figure 1 below.

Figure 1: Precipitation Pattern from 1971-2000

for Jamaica.

Prepared by the Climate Branch

Meteorological Service, Jamaica 65 ¾ Half Way Tree Road

Kingston 10 Telephone: 929-3700/3706

Email: datarequest@metservice.gov.jm

Climate Branch March 2019

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HIGHLIGHTS FOR MARCH

Parish Mean Rainfall and Comparison with 30-yr Averages

MAR MAR MAR % OF 30 YR NORMAL

Parishes KEY 2019 2018

30 YR

NORMAL

(1971-

2000)

2019 2019 2019

JAN FEB MAR

Hanover HAN 118 63 104 69 62 114

Westmoreland WES 119 76 88 110 72 135

Manchester MAN 123 85 91 127 138 136

St. Elizabeth STE 89 103 99 80 38 90

Clarendon CLA 66 29 56 89 60 118

St. Catherine STC 125 28 61 129 65 206

Trelawny TRE 151 74 61 118 41 249

St. James STJ 119 57 60 149 55 197

St. Ann STA 117 79 71 57 37 165

St. Mary STM 67 113 108 41 37 62

Portland POR 144 212 209 36 41 69

St. Thomas STT 78 22 68 52 136 114

Kgn. & St.

And. KSA 44 20 67 72 35 66

Jamaica JAM 105 75 88 70 58 119

Table 1: Parish Mean Rainfall and Comparison with 30-yr Averages

Nine of thirteen parishes received above-normal rainfall.

Two (2) of thirteen (13) parishes recorded meteorological

drought.

Near-normal to above-normal rainfall is forecast for the

island, for April to June.

Above-normal temperatures are forecast for the next

three months

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Rainfall Assessment

For March 2019, nine (9) of thirteen (13) parishes1 namely Westmoreland, Manchester,

Clarendon, St. Catherine, St. Thomas, St. Ann, Trelawny, St. James and Hanover recorded

above-normal rainfall and the other 4 parishes namely St. Elizabeth, Kingston & St. Andrew

(KSA), Portland and St. Mary recorded below-normal rainfall. Ten of 13 parishes received more

rainfall in March 2019 when compared to March 2018; while the other three parishes namely, St.

Elizabeth, Portland and St. Mary received less rainfall this March compared to one year ago.

The percentages of mean rainfall in March were higher for twelve parishes when compared to

those of February. Only Manchester had a slightly lower percentage of rainfall when doing a

similar comparison however, for a 4th consecutive month, the parish has recorded rainfall of

more than 100% of its 30-year monthly normal.

No parish recorded 50% or less of their 30-year mean in March 2019, which is traditionally the

driest month for Jamaica. However, two parishes; namely St. Catherine and Trelawny received

more than 200% of their monthly normal rainfall.

Overall, Jamaica’s average rainfall for March was 105 mm, which is 30 mm more than that

received one year ago and this represents 119% of the 30-year (1971-2000) mean monthly value.

Across the island, the March rainfall ranged from 62% of the 30-year normal for St. Mary to

249% for Trelawny.

1 Note that Kingston and St. Andrew (KSA) are combined and

reported as one parish.

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Fig.2. Distribution of Jamaica’s Rainfall for March 2019

Fig.3. Mean Island Rainfall for March

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.

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Droughts are regional in extent and each region has specific climatic characteristics2. For the

Caribbean region, a meteorological drought event occurs any time the SPI is negative for at least

2 consecutive months and reaches values of:

-0.80 or less from November to April or

-1.30 or less from May to October or

-1.00 for October/November and April/May.

The MSJ calculates an observed SPI using a 2-month time interval and reports on drought

conditions using bi-monthly intervals. Results, by parish, are presented in Table 2.

Parish Standard Precipitation Index (SPI) Assessment

Observed SPI for December 2018 to March 2019

Parishes Dec/Jan Jan/Feb Feb/Mar

Westmoreland 0.16 0.39 0.71

St. Elizabeth 0.08 -0.58 -0.25

Manchester 0.50 0.11 0.29

Clarendon -0.07 0.27 0.34

St. Catherine 0.59 0.30 0.93

Kingston & St. Andrew -0.64 -0.52 -0.50

St. Thomas -0.40 -0.54 0.26

Portland -1.35 -2.09 -0.89

St. Mary -1.44 -1.71 -0.81

St. Ann -0.90 -1.33 0.04

Trelawny -0.38 -0.11 0.66

St. James 0.23 -0.10 0.40

Hanover -0.58 -0.34 0.55

Table 2: Parish SPI for December 2018 to March 2019

2 World Meteorological Organization, 2012: Standardized Precipitation Index User Guide (M. Svoboda, M. Hayes and D. Wood).

(WMO-No. 1090), Geneva.

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Table 3: Severity Classes of the SPI

SPI Discussion

For the February/March period, all 13 parishes recorded increases in their SPI values with, St.

Ann and Portland recording the 2 largest movements in values; while Kingston & St. Andrew

(KSA) and Clarendon recorded the least increases in their SPI values.

During the February/March period, there were four parishes which recorded SPI values equating

to rankings ranging from abnormally wet to moderately wet conditions while, there were two

parishes which recorded moderately dry conditions. The remaining seven parishes recorded near-

normal (wet or dry) conditions during the same period. Based on the drought criteria, the

parishes of St. Mary and Portland continued to experience meteorological drought conditions and

this, for a 4th consecutive bi-monthly period.

For a 2nd consecutive bi-monthly period, Portland has recorded the lowest SPI value, with -0.89

(moderately dry) for the February/March period; representing a change of 3 severity classes

when compared to the January/February period. St. Ann also recorded improved conditions as,

the parish’s SPI values changed 4 severity classes, moving from severely dry in

January/February to near-normal (wet) in February/March. This means that the parish was above

the drought classification for this bi-monthly period. The parishes which recorded wet conditions

were, St. Catherine (moderately wet) and Westmoreland, Trelawny & Hanover, with abnormally

wet conditions,.

Of the remaining 6 parishes with near-normal conditions, there were two, KSA and St. Elizabeth

with negative SPI values while, the other 4 parishes namely; Manchester, Clarendon, St. Thomas

and St. James recorded positive SPI values. Generally, all parishes were better off, in relation to

SPI Value Category SPI Value Category

0.00 to -0.50 Near-normal (dry) 0.00 to 0.50 Near-normal (wet)

-0.51 to -0.79 Abnormally Dry 0.51 to 0.79 Abnormally Wet

-0.80 to -1.29 Moderately Dry 0.80 to 1.29 Moderately Wet

-1.30 to -1.59 Severely Dry 1.30 to 1.59 Severely Wet

-1.60 to -1.99 Extremely Dry 1.60 to 1.99 Extremely Wet

-2.00 or less Exceptionally Dry 2.00 or more Exceptionally Wet

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drought conditions, with higher indices than for the previous assessment period in

January/February.

Fig.4. SPI Analysis for February-March 2019

Precipitation and Temperature Outlook: April to June 2019

For the upcoming period April to June, rainfall amounts are likely to be near-normal to above-

normal based on the findings from our seasonal climate forecast models. Through the period

there was an increase in forecast confidence, with most stations likely to receive higher than

normal rainfall with warmer temperatures, when compared with historical records.

Forecast Verification

For the same period last year, April-June 2018, the models performed generally fair, with

accuracy in the range of 33-60 percentage points. The initial forecast indicated that rainfall was

likely to be below-normal for 4 selected stations, of which three materialized. Two other selected

stations were expected to receive near-normal rainfall for the period; one station achieved this.

The remaining 11 selected stations were forecast to receive above-normal rainfall however, only

two stations attained this.

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Summary

Nine of 13 parishes recorded rainfall amounts that were above their respective 30-year (1971-

2000) monthly means during March. For a 4th consecutive month, Manchester has recorded

rainfall of more than 100% of its 30-year normal.

March is traditionally the driest month for Jamaica however, the island recorded 119% of its 30-

year normal rainfall during the month. This above-normal rainfall was achieved because 7

parishes recording more than 100% of their 30-year normal rainfall and another two parishes

recorded over 200% of their monthly means. It should be note that no parish recorded 50% or

less of their monthly normal during March 2019.

Conditions showed improvements for all 13 parishes, however, despite this occurring, St. Mary

and Portland continued to record meteorological drought conditions, with both parishes doing

so for 4 consecutive bi-monthly periods.

The projection over the next 3 months (April to June), which includes the early wet season, is for

near-normal to above-normal rainfall across the island.

Should this forecast materialize, it could bring temporary relief to areas in the drought-stricken

parishes of St. Mary and Portland, as well as, to areas in other parishes which are experiencing

dry conditions. However, the expected rainfall may not be sufficient to reverse the deficits in

amounts being experienced across the island during 2019 and in particular, for St. Elizabeth,

KSA, Portland and St. Mary.