Hurricane Sam Continues To Rapidly Strengthen, Swells To Affect Lesser Antilles

What you need to know:
– Sam is forecast to move northeast of the Lesser Antilles, safely northeast of the Leeward Islands, posing no direct threat to T&T and the Lesser Antilles.
– The National Hurricane Center is forecasting Sam to remain at Category 4 strength, with fluctuations in intensity through the next 48 hours.
Swells from Hurricane Sam are forecast to affect the northern and eastern coastlines of the Lesser Antilles through the week.
– Due to near calm winds induced by Sam, very hot temperatures are forecast across the region with localized, slow-moving afternoon showers and thunderstorms across western and hilly areas.

What we know

Hurricane Sam's Forecast Track as of 11:00 PM Saturday 25th September 2021. (National Hurricane Center)
Hurricane Sam’s Forecast Track as of 11:00 PM Saturday 25th September 2021. (National Hurricane Center)

Hurricane Sam remains a compact but powerful tropical cyclone well east of the Lesser Antilles, approximately 1,300 kilometers east-northeast of Trinidad and Tobago. Tropical-storm-force winds are extending 165 kilometers outward from the center while hurricane-force winds extend 45 kilometers outward.

Based on the latest information from the National Hurricane Center (NHC), the center of Hurricane Sam was located near 13.5°N, 49.0°W. Sam is moving toward the west-northwest near 13 KM/H and this general motion is forecast to continue through Sunday. A turn toward the northwest is expected on Monday.

Sam now has maximum sustained winds near 230 KM/H with higher gusts, making it a Category 4 hurricane on the
Saffir-Simpson Hurricane Wind Scale. Fluctuations in intensity are likely into early next week.

Sam has continued to intensify over an area with warm sea surface temperatures between 28°C and 29°C, low wind shear, and favorable upper-level winds.

Hurricane Sam, East of the Lesser Antilles, in the Atlantic Ocean. (Weathernerds)
Hurricane Sam, East of the Lesser Antilles, in the Atlantic Ocean. (Weathernerds)

Where is Hurricane Sam Going?

The takeaway: Hurricane Sam’s forecast track takes it northeast of the northernmost Leeward Islands. Given Sam’s small size and the higher confidence of the eventual track, direct impacts are not expected with periphery rain bands affecting those islands remain unlikely at this time. This system poses no direct threat to the Windward Islands, including Trinidad and Tobago at this time.

Hurricane Sam's forecast tracks from top dynamical and consensus hurricane models as of 8:00 PM Saturday 25th September 2021. (NCAR)
Hurricane Sam’s forecast tracks from top dynamical and consensus hurricane models as of 8:00 PM Saturday 25th September 2021. (NCAR)

Hurricane Sam continues to move along the southern periphery of a large and strong high-pressure ridge to the northeast and north, which is now shifting east. A deep-layered trough system is now moving and strengthening over the western Atlantic which will allow for Sam to move northward at a faster forward speed.

The latest track forecast, as well as all ensemble models, have shifted noticeably eastward tonight. This steering pattern is expected to take the hurricane northwestward, missing the Lesser Antilles.

Looking at the two top global models, the American GFS and the European EMCWF, both take the tropical cyclone well northeast of the Leewards. Sam is forecast to make its closest approach to the Leewards between Tuesday night and Wednesday night.

Hurricane Sam: The Intensity

The takeaway: Sam has reached its near-peak intensity at Category 4 strength, with fluctuations in intensity through the next 48 hours. Sam is forecast to slowly weaken to Category 3 by Wednesday.

Hurricane Sam's forecast tracks from top dynamical and consensus hurricane models as of 8:00 PM Saturday 25th September 2021. (NCAR)
Hurricane Sam’s forecast tracks from top dynamical and consensus hurricane models as of 8:00 PM Saturday 25th September 2021. (NCAR)

Sam has likely reached near peak intensity at Category 4 strength, but fluctuations up and down in intensity are still possible.

Radar images from the reconnaissance aircraft indicated that the eyewall was thin in many locations due to dry-air intrusions. Sam will be located in a relatively dry mid-level environment, allowing for more intruding dry air. Further, the depth of warm water below Sam is fairly shallow. As Sam slowly moves west-northwest, cooler water below may be churned and further contribute to weakening. Wind shear, though light through Tuesday, is forecast to increase from Wednesday onward. Lastly, eyewall replacement cycles are likely to occur.

These factors will likely contribute to Sam’s fluctuation but general, slight, weakening over the next several days but as the powerful hurricane moves faster northwestward, it will encounter more warm waters capable of sustaining its major hurricane strength.

Hurricane Sam's probabilities for hurricane-force winds as of 11:00 PM Saturday 25th September 2021. (National Hurricane Center)
Hurricane Sam’s probabilities for hurricane-force winds as of 11:00 PM Saturday 25th September 2021. (National Hurricane Center)

What impacts can we expect to see from Tropical Storm Sam?

Based on the latest track, feeder band activity is not expected across the Lesser Antilles, including the Leewards. Swells are forecast to affect the entire island chain from Monday through the upcoming week. Sam will also influence winds across the island chain, allowing for hot temperatures, anomalous southerly winds through Wednesday, and localized afternoon showers/thunderstorms in western areas.

Hurricane Sam's probabilities for tropical-storm-force winds as of 11:00 PM Saturday 25th September 2021. (National Hurricane Center)
Hurricane Sam’s probabilities for tropical-storm-force winds as of 11:00 PM Saturday 25th September 2021. (National Hurricane Center)

Sam is forecast to move well northeast of the Lesser Antilles between Tuesday and Wednesday. Due to the small radius of circulation, feeder band activity is unlikely to affect the region, including the Leeward Islands.

Still, long-period swells are likely to begin affecting coastlines of the Lesser Antilles from Monday 27th September 2021 through the upcoming week, which can produce life-threatening surf and rip currents.

As Hurricane Sam moves northeast of the Leewards, a trough extending from the cyclone’s core to the southwest will slacken the pressure gradient, causing light winds. Temperatures across Trinidad and Tobago may near record highs for 2021. Light winds, high moisture, and a somewhat favorable atmospheric setup will allow for high temperatures triggering localized, slow-moving afternoon showers and thunderstorms across western and hilly areas. In addition, funnel clouds and waterspouts will also be possible.

Specifically for Trinidad and Tobago, in addition to the localized activity outlined above and the long-period swells, winds from the south are forecast. This wind profile will result in showers and thunderstorms moving from the south to the north, possibly intensifying over the Gulf of Paria and the Northern Range and producing hazardous seas as well as street/flash flooding along the East-West Corridor and along western Trinidad.

But this model shows…

Individual model runs are just one possible outcome from a myriad of outcomes. Weather does not always follow what is modeled, and even what may be forecast. Beware of individual model runs being posted on social media.

Always check the National Hurricane Center for the latest information for tropical cyclones and your local meteorological offices for country-specific advisories.

What should I do?

This system is not forecast to directly affect the Southern Windward Islands, including Trinidad and Tobago. Don’t panic. There are no immediate or direct tropical storm threats heading to T&T, so feel free to ignore the “storm coming” chain messages that pass through WhatsApp every hurricane season.

If you are a risk-averse person, now is a good time to check your inclement weather, flood, or hurricane season plan, ensuring your preparedness supplies are not expired, stocked, and in a safe location.

The Office of Disaster Preparedness and Management has compiled a comprehensive guide for preparing for the Wet and Hurricane Season.

Tropical Cyclone Climatology

2021 has already produced 19 tropical cyclones in the Atlantic Basin, with the following system being named Victor for the 2021 Atlantic Hurricane Season.

As we head through the second half of September and into October, we’ll continue to monitor the entire Atlantic closely as tropical cyclones could form from tropical waves, non-tropical low-pressure systems in the North Atlantic, and from the Central America Gyre in the Western Caribbean Sea or the southwestern Gulf of Mexico.

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