Cayman under drought warning

Hotter days, limited rainfall expected

Despite some recent rainy days, over the past few months, Cayman has been experiencing hotter, drier weather than usual, leading to the issuing of a drought warning.

National Weather Service meteorologist Avalon Porter expects those conditions will likely continue over the coming months.

National Weather Service’s Avalon Porter

Porter, in an interview via Zoom with the Cayman Compass, said Cayman is shifting to warmer summertime conditions and with that comes the heat.

“There will be hotter conditions for people to have to look out for or take precaution for; I wouldn’t say heat stroke, but heat stress [is] occurring, now that we are going into our summertime,” Porter said.

He said there is a possibility of ‘heat wave’ days in the next two to three months, but he does not expect those to be frequent.

Drought warning in effect
The National Weather Service recently issued its monthly climate bulletin, which indicated that ‘moderate or worse’ drought has developed in Cayman and a long-term drought warning is in effect.

With most people shuttered at home due to the COVID-19 pandemic, the effects of the heat may be felt through higher CUC bills driven by increased use of air conditioning.

According to the bulletin, “the rising temperatures and the possibility of heat waves into July will make the heat uncomfortable at times. There are relatively strong indications that August to October may be wetter than usual across Cayman.”

For the next three months though, Porter said, the dry days will outnumber the wet ones.

“The drought warning usually uses something called a ‘standard precipitation index’, and that gives you an idea about whether you’re above your normal rainfall or below, based on the rainfall totals for the past months. So, you have your index for three months, six months, or 12 months. If we look at our one for six months and 12 months, it shows us that we’re in the area that is dry,” Porter said.

The bulletin projected that rainfall totals from May to July are likely to be “at least as wet as usual” for Cayman.

“May and June usually [experience] frequent heavy showers. July’s wet season often includes a mid-summer dry spell,” the report said.

While rainfall has been sporadic throughout the islands, Cayman’s short-term drought can end with a few torrential downpour days, but Porter said the long-term, or meteorological, drought will not go away so easily.

“If you have heavy rain in May, June and July, those months may come up to the average, but we still have a [rainfall] deficit,” he said.

The deficit was created due to low rainfall levels over the last few months.

Porter said while droughts are a concern, Cayman does not rely on reservoirs for its water supply so it should not create a problem.

However, he said it may pose a challenge for farmers who use well water for irrigation as those wells may be in a deficit from the last year.

“They might see the salinity of the water increase,” he added.

For homeowners, he said, they may have to add a few more dollars to their water bills as they will have to water their plants more.

Cayman did experience two days of torrential downpour late last month, which Porter said was welcomed but only about 100 millilitres of rain was recorded.

As for discontinuing the drought warning, Porter said, the rainfall would have to be enough to cover the deficit.

“It depends on the numbers [which] might give you some good rainfall,” he said, but added it won’t help the farmers if it rains one or two days and then the rest are dry. “We have to see what the rest of the month says,” he said.

Historically, in May, June and July, there are about three to five dry spells. The forecast indicates an additional dry spell, for an expected total of up to six, may occur over the next three months.

Dry spell: 

A dry day is day in which the rainfall was less than 1 mm. A seven-day dry spells is seven days without rain (<1mm). So a forecast of two to three, seven-day dry spells means about two to three sets of seven days without rain.

Short-term drought uses the rainfall for the past three months and the three-month forecast (May-June-July).

Long-term drought uses the rainfall for the past nine months and the three-month forecast (end of May).

Report projections:

Frequency of seven-day dry spells: Historically, over May, June and July, there are about three to five dry spells. The forecast indicates about three to six for the next three months.

Frequency of 10-day dry spells: One to two dry spells occur over May, June and July. The forecast indicates one to three dry spells.

Rainfall: The usual rainfall range for January to March at Owen Roberts International Airport is 84.1 mm to 133.6 mm. From January to March 2020, the total rainfall was 66.6 mm, which was below the normal range.

The usual rainfall range for May to July is 381.5 mm to 494.5 mm. The May-July 2020 outlook calls for 50% probability of above-normal rainfall.

Frequency of wet days: Historically, over May, June and July, there are about 24 to 36 wet days. The forecast indicates about the same for the next three months.

Frequency of seven-day wet spells: Between three and six wet spells occur from May to July. The forecast indicates about the same number of wet spells for Cayman this year.

Frequency of extreme (top 1%) three-day wet spells: The forecast indicates the number of extreme wet spells might range from zero to two.

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