The Adverse Weather Alert
The Trinidad and Tobago Meteorological Service has issued an Adverse Weather Alert as Tropical Wave 32 nears Trinidad and Tobago, interacting with the ITCZ and bringing light southerly winds across the island. Heavy showers and thunderstorms are likely, according to the TTMS to after 5:00 AM Monday 5th August 2019 through 2:00 PM Tuesday 6th August 2019.
Note that due to favorable atmospheric conditions, locally severe thunderstorms are possible, producing heavy rainfall and gusty winds, particularly along the southward facing slopes of the Northern Range.
Although this alert has been issued by the TTMS beginning at 5:00 AM tomorrow, through 2:00 PM Tuesday, showers and thunderstorms are possible before this alert begins (as in through the evening today, on Sunday), as well as through the second half of Tuesday and even on Wednesday, due to favorable conditions in place.
Trinidad and Tobago is NOT under any tropical storm threat, watch or warning.
Based on the latest model guidance, these showers, with isolated heavy showers and thunderstorms may produce severe weather across Trinidad and Tobago. Street flooding, flash flooding, particularly across Northern and Central Trinidad where showers and thunderstorms may continue to move across. Gusty winds are likely in the vicinity and during heavy showers or thunderstorms. These gusty winds and heavy rainfall will be capable of triggering landslides in landslide-prone areas, as well as downing trees and utility poles. See below for more details on what impacts to expect.
Information from the Trinidad and Tobago Meteorological Service concerning the Adverse Weather Alert for August 5th-6th, 2019.
“Heavy showers or thunderstorms will occur in few areas mainly during the daytime in North and Central Trinidad. Street or Flash flooding will occur in these areas. There is a high possibility of landslides or landslips along the Northern Range.” according to the Trinidad and Tobago Meteorological Service. This “alert” status takes into account the possibility of the event occurring. This adverse weather event is likely.
The color of the watch indicates the severity of the event and the probability of the event occurring. Currently, the alert level is at Yellow. This means that the hazard is possible to be aware of the impacts of Street/Flash Flooding and Gusty Winds in your area. Areas prone to landslides should also be aware of the hazard and impacts.
The 32nd tropical wave of the 2019 Atlantic Hurricane Season is still east of Trinidad and Tobago as of 4:00 PM Sunday 4th August 2019.
What to Expect Over Next 24-72 Hours
The Takeaway: Scattered showers and thunderstorms are forecast to move across mainly Northern and Central Trinidad on over the next 24-72 hours. Isolated showers are also possible across Southern Trinidad and Tobago, but severe weather is likely across the northern half of the coutnry due to weak, southerly winds.
Generally, widespread severe weather is not likely. Localized to scattered severe weather reports are possible, with landslides across the Northern Range and street/flash flooding across the East-West Corridor likely.
Presently, winds are from the south to southeast at low-levels. This is slowly moving showers mainly from northward, instead of the usual westward motion. A lull in activity is forecast later this evening, with showers and thunderstorms forecast yet again to begin across the island early Monday morning.
Similar to Sunday, periods of sunshine are forecast to be interrupted by showers and thunderstorms across mainly the Northern half of Trinidad and the southern half of Tobago, with hot, humid and sunny conditions prevail across the Southern half of Trinidad and northern half of Tobago.
Based on the latest model guidance, showers, periods of rain and thunderstorms are forecast to affect mainly Trinidad over the next three days, though the adverse weather alert is only through Tuesday.
Light winds persisted across Trinidad and Tobago today, forecast across the region over the next 2-3 days. Light winds from the south to southeast allowed for favorable low-level convergence to develop across Trinidad when coupled with daytime heating. High amounts of atmospheric moisture fuelled convection and with relatively weak wind shear, heavy showers and thunderstorms flourished.
In addition, these light (weak) winds at low levels resulted in the slow movement of these showers and thunderstorms. This allowed for high rainfall accumulations across interior Central Trinidad and along the south-facing slopes of the Northern Range, along the East-West Corridor.
Lastly, since winds were moving across Trinidad (and Tobago) from the south, the Northern Range forced air upwards, called orographic lift. This phenomenon, simply put, aid in the development of showers, or enhance showers and thunderstorms. The latter was the case today across the Northern Range.
With all these features coming together, showers and thunderstorms persisted across mainly Trinidad throughout the day, dumping copious amounts of rainfall across the East-West Corridor, resulting in street and flash flooding across many major roadways in the North-Central area. Similar conditions are forecast over the next several days.
Locally Heavy Rainfall & Flooding: Based on the latest model runs on Sunday evening, from Sunday (2:00 PM) through Thursday (2:00 AM), generally, over the 60 hour period, models are in agreement of fewer than 40 millimeters across Southern halves of Trinidad and Tobago and between 40-60 millimeters across the northern half of Trinidad. Isolated rainfall totals up to 100 millimeters are possible across Central locations of Trinidad.
Generally, with heavy showers and thunderstorm activity, street flooding, particularly in flood-prone areas or areas with poor drainage, is possible as well as flash flooding in areas where more prolonged heavy rainfall may occur, based on the above-mentioned forecast rainfall totals.
Frequent Lightning: In addition, with thunderstorms, frequent lightning is likely. As of midnight, through 4:20 PM, over 4000 lightning strikes have occurred near Trinidad and Tobago, with 3175 being dangerous cloud to ground strikes.
Gusty Winds: Gusty winds, generally between 40 and 50 KM/H are possible Gusty winds are most likely prior to, in the vicinity of, or occur during heavy showers or thunderstorms. With wind gusts up to 50 KM/H, whole trees are expected to be in motion and there may be some inconvenience when walking against the wind gusts. Light outdoor objects may topple or become airborne such as garbage cans, potted plants, loose galvanize or construction material and other outdoor furniture. Tents may jump. Older/weaker trees may fall.
Landslides: Heavy showers across the Northern Range may trigger landslides in landslide-prone areas. Particularly in areas that receive heavy rainfall, landslides and/or mudflows may occur across both islands. These landslides, in addition to gusty winds, may down trees, utility poles and impede traffic on roadways.
Why I May Not/Will Not See Constant Rainfall?
A frequent complaint is the forecast is wrong because I didn’t experience any rainfall. Scattered showers mean that you, individually, may experience some showers intermittently throughout the day and there is a higher chance for this activity than isolated activity.
Generally, because of winds associated with tropical waves, showers and thunderstorms tend to follow a west-northwest track, generally missing areas across Southwestern Trinidad and even Northwestern Trinidad – though activity due to local climatic effects such as daytime heating may trigger shower and thunderstorm development across these areas. See the below graphic for a simple explanation.
With this tropical wave (Tropical Wave 32), mostly scattered showers are forecast. Hence, we are likely to see intermittent showers and thunderstorms, interrupting partly cloudy to overcast skies between Sunday and Wednesday.