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A satellite image of Saharan dust over the Caribbean.
A satellite image of Saharan dust over the Caribbean.
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By Kenton X. Chance

GEORGETOWN, Guyana (CMC) – The Barbados-based Caribbean Institute of Meteorology and Hydrology (CIMH) says regional forecasters are trying to improve forecasting of Saharan dust intrusion, in light of its impact on weather and health.

CIMH said some places across the region receive as much as one millimetre of Saharan dust during an intrusion event.

“As long as it’s thin enough, small enough grains, it can be flying over and deposit as soon as the winds slacken,” CIMH climatologist,Cédric Van Meerbeeck, told the Caribbean Climate Outlook Forum (CariCOF) that ends here later on Friday.

He said regional forecasters are trying to answer “the million dollar question” of forecasting long in advance, the movement of Saharan dust from Africa to the Caribbean.

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Currently, the CIMH can only forecast Saharan dust intrusion up to two weeks in advance.

“There are some things we understand about it. For instance, the reason why it increases from early on in the year up to about May to July when it peaks, typically in the year is because of the winds that blow over Africa,” Van Meerbeeck said.

He explained that the Intertropical Convergence Zone (ITCZ) — the area where the northeast and the southeast trade winds converge — is basically a thermal equator that moves with the seasons.

“Because it moves with the seasons, once it goes over the Sahara, the trade winds intensify, picking up dust and going across the Atlantic,” he said, adding that this is “the general theory.

“What we cannot presently do is understand with the variability of that seasonal movement of this ITCZ how exactly does that influence when we are getting or not getting dust coming into the Caribbean,”  Van Meerbeeck said.

He said the CIMH can forecast the movement of dust accurately up to two weeks in advance and uploads the data to its website twice daily.

“So that is available, but just not for the seasonal timescale. So unfortunately, it’s still in the realm of research, and the code has not been cracked yet,” Van Meerbeeck said.

The climatologist was fielding questions at the forum during the CIMH announcement that it was forecasting a “hyperactive” 2004 Atlantic Hurricane Season with up to 29 named storms, 13 of which are likely to become hurricanes, including seven major hurricanes.

The institute, however, said that Saharan dust would impact cyclone activity in the region.

Van Meerbeeck explained that the Saharan dust affects the atmospheric temperature in the region and temperature affects cyclones.

“… the most important way that dust can interfere with the heat is, whenever you have dust overhead, what’s going to happen is that you’re going to get the atmospheric motion though, the winds vertically come down,” he said, adding that this means that the more air is compressed toward the surface of the earth.

He likened it to inflating a tyre, noting that doing so produces heat.

“So we get even more heat sticking to the surface, along with humidity when there’s dust overhead. So the more dust episodes we will get, the more excessive heat we will feel.”

Kingstown Bequia
The northern Grenadine island of Bequia cast a faint outline on the horizon on May 10, 2024, as visibility was reduced by Saharan dust.

The climatologist, however, said that the Saharan dust has the opposite effect on sea surface temperatures.

“Fortunately, on the sea temperatures, it has the opposite effect. And why is that? because the dust actually acts a bit as a shield from sunlight. And it’s the sunlight hitting the ocean that warms it up,” Van Meerbeeck said.

“So in the long run, we hope that there’s a little bit of a cooling effect on the ocean, and therefore a mitigating effect on this extreme nature of the season going forward. I doubt that that will be strong enough to negate that heat that’s currently in the ocean…”

Van Meerbeeck said that Saharan dust has a similar cooling effect on tropical cyclones, noting that a cyclone survives on humidity and Saharan dust is dry air.

“If you drive dry air into a storm, no matter how strong that storm is, but particularly the stronger storms, it will weaken it,” he said, adding that dust seriously weakened a category 5 storm before it reached the Lesser Antilles last year.

Regarding what happens if dust continues to be frequent during the peak of the hurricane season, Van Meerbeeck said, “I know we’re in uncharted territories. But if you look at the historical record, the impact, or the number of times that dust impacts the hurricane season activity after August is really much lower, if at all.”

He said this means that the effect of dust, which forecasters do not know currently, creates uncertainty up to August.

“After that, there is no doubt in all the forecasts. That doesn’t mean that there’s nothing we don’t know. But there’s no doubt and all the forecasts so far, that is going to be extremely active.”

Meanwhile, the CIMH head of meteorology and hydrology, Adrian Trotman, said the institute was partnering with the European Union to examine the major health impact of Sahara dust.

Trotman said that in April, a renowned pulmonologist in Barbados suggested that over the past few years, not only had the Saharan dust started earlier than was typically the case, but that more people were developing asthma late in life.

“She said that’s unprecedented. And she specifically put the finger on Saharan dust  as one of the major causes of that late-in-life development of asthma.”

Trotman said this shows that the CIMH’s Sharan dust forecast, although it is limited currently to two weeks in advance, “is going to be really important.

“And if you want the science to be driven by research, it’s up to you in the health sector to push this,” he took participants in the forum, which brought together professionals from various sectors, including water, health, disaster management and tourism.

“Say to authorities, ‘Listen, there’s enough evidence from research that Saharan dust is triggering major development of asthma late in life,’” Trotman said.

He said that if people do not know they have asthma, they are likely to die of it because they might not have an inhaler when they suffer an attack.

“… because you’re not accustomed, you never had it. And you’re always thinking that if I never had it early in life, I most likely won’t. But that’s changing. Like the climate, that’s changing.”

Van Meerbeeck pointed out that in addition to asthma as a result of Saharan dust, wildfire smoke is also an issue during the late dry season.

“Sometimes, it’s a smoke or often the combination of the two,” he added.

One reply on “Scientists working to improve Saharan dust forecasting”

  1. Take warning says:

    Thats why I always keep a Becotide and a ventolin inhaler and keep a portable nebulizer in my home . I am not an asthmatic but had worked on various respiratory units . Along with the Sarahan dust, there are lots of burning in communities , especially the toxic smell of tyres, old clothes and whatever else. There are elderly people who have to inhale this toxic fumes for
    hours ,. This is a regular habit in a cummunity above kingstown. Pray the authorities will look into these practices and do something about it ASAP.

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