Tropical Storm Gonzalo Forecast to Bring Adverse Weather to T&T, Windwards

Tropical Storm Gonzalo Key Messages:
– Watches & Warnings: Tropical Storm Watches are in effect for Grenada and Tobago. Hurricane Watches are in effect for Barbados and St. Vincent and the Grenadines. Additional watches and warnings may be issued on Friday
– Track: The track for Gonzalo has slowed somewhat, and shifted slightly. Tropical Storm Gonzalo is forecast to move across the region on Saturday into Sunday., with the track of the center of the system still moving north of Tobago.
– Intensity: There is great uncertainty in the intensity for this tropical storm. Presently, it is expected to strengthen into a hurricane on Thursday, remaining a hurricane as it moves north of T&T on Saturday with sustained winds of up to 120 KM/H and gusts to 150 KM/H. Across Trinidad, wind gusts in excess of 65 KM/H are likely in heavier showers or thunderstorms. Across Tobago, wind gusts in excess of 85 KM/H are expected.

Key Messages for Tropical Storm Gonzalo as of 11:00 PM Thursday 23rd July 2020 for Tobago.
Key Messages for Tropical Storm Gonzalo as of 11:00 PM Thursday 23rd July 2020 for Tobago.

Rainfall: As of Thursday night, direct and indirect impacts are forecast. Slight adjustments in the track may have significant changes in the rainfall forecast. Isolated heavy rainfall will still be possible across T&T. Generally, between 25-50 millimeters of rainfall forecast Friday through Sunday, with isolated totals in excess of 100 millimeters in areas of persisting heavy rainfall and thunderstorm activity, mainly across Northern, Eastern Trinidad and Tobago.
Street flooding and flash flooding in heavy to violent showers and thunderstorms. There is a low chance of riverine flooding. There is the medium to high risk of landslides, particularly across Tobago.
– Seas, mainly on Saturday, forecast to be moderate to rough, with waves up to 3.0 meters, occasionally up to 4.0 meters in open waters. In sheltered areas, up to 1.5 meters and choppy.

Key Messages for Tropical Storm Gonzalo as of 11:00 PM Thursday 23rd July 2020 for Trinidad
Key Messages for Tropical Storm Gonzalo as of 11:00 PM Thursday 23rd July 2020 for Trinidad

NHC: Gonzalo To Affect Windwards on Saturday

Tropical Storm Gonzalo's Official Forecast Track from the National Hurricane Center as of 11:00 PM AST Thursday 23rd July 2020.
Tropical Storm Gonzalo’s Official Forecast Track from the National Hurricane Center as of 11:00 PM AST Thursday 23rd July 2020.

The National Hurricane Center, as of 11:00 PM, continues to issue advisories on Tropical Storm Gonzalo, 1,170 KM east of the Windward Islands.

At 11:00 PM AST, the center of Tropical Storm Gonzalo was located near latitude 9.9 North, longitude 50.6 West. Gonzalo is moving toward the west near 14 MPH (22 KM/H). A westward to west-northwestward motion with an increase in forward speed is expected through the weekend. On the forecast track, the center of Gonzalo will approach the southern Windward Islands Friday night and move across the islands Saturday and into the eastern Caribbean Sea Sunday.

Maximum sustained winds are near 60 MPH (95 KM/H) with higher gusts. Some strengthening is forecast during the next day or two, and there is still a chance that Gonzalo could become a hurricane. Weakening is expected after Gonzalo moves into the Caribbean Sea and the cyclone is expected to dissipate by the middle of next week.

Tropical-storm-force winds extend outward up to 25 miles (35 KM) from the center. This is a compact cyclone. 35 KM is just under the distance from Grand Bazaar to San Fernando in Trinidad. The estimated minimum central pressure is 1000 millibars.

Three Aircraft Reconnaissance flights are scheduled for Friday into Gonzalo, with the first planned to take off at 5:30 PM local time. This will provide forecasters with integral data on the actual strength of the tropical cyclone, as well as more precise data for modelling.

Most Likely Arrival Time: the graphic that identifies the time before or after which the onset of tropical-storm-force winds is equally likely. This graphic would be more appropriate for users who are willing to risk not having completed all their preparations before the storm arrives. (NHC)
Most Likely Arrival Time: the graphic that identifies the time before or after which the onset of tropical-storm-force winds is equally likely. This graphic would be more appropriate for users who are willing to risk not having completed all their preparations before the storm arrives. (NHC)

Hazards Affecting Land

WIND: Hurricane or tropical storm conditions are possible within the respective watch areas on Saturday.

RAINFALL: Gonzalo is expected to produce total rain accumulations of 2 to 5 inches (50 to 125 mm), with isolated maximum amounts of 7 inches (175 mm) in Barbados and the Windward Islands from Friday night through Sunday night. Gonzalo is also expected to produce total rain accumulations of 1 to 2 inches (25 to 50 mm) in Trinidad and Tobago. Rainfall in Barbados and the Windward Islands could lead to life-threatening flash floods.

Watches & Warnings

Tropical Storm Gonzalo Watches & Warnings as of 11:00 AM Thursday 23rd July 2020.

A Hurricane Watch is in effect for:

  • Barbados
  • St. Vincent and the Grenadines

A Tropical Storm Watch is in effect for:

  • Tobago
  • Grenada and its dependencies
Tropical Storm Watch for Tobago from the Trinidad and Tobago Meteorological Service for Tobago as of 12:10 AM Friday 24th July 2020. (TTMS)
Tropical Storm Watch for Tobago from the Trinidad and Tobago Meteorological Service for Tobago as of 12:10 AM Friday 24th July 2020. (TTMS)

A Hurricane Watch means that hurricane conditions are possible within the watch area. A watch is typically issued 48 hours before the anticipated first occurrence of tropical-storm-force winds, conditions that make outside preparations difficult or dangerous.

A Tropical Storm Watch means that tropical storm conditions are possible within the watch area, generally within 48 hours.

Interests elsewhere in the Windward Islands should monitor the progress of this system. Additional watches or warnings will likely be required for some of these islands tonight or on Friday.

What We Know

Tropical Storm Gonzalo in the Central Atlantic, producing a concentrated area of strong convection near the center of circulation Thursday night (Weathernerds)
Tropical Storm Gonzalo in the Central Atlantic, producing a concentrated area of strong convection near the center of circulation Thursday night (Weathernerds)

Tropical Storm Gonzalo continues to produce a compact area of moderate to strong convection in the Central Atlantic, well east of Trinidad and Tobago.

After ingesting a hefty portion of dry high statically stable air (Saharan Dust) this morning, Gonzalo appears to be on the comeback trail. Enhanced infrared BD-curve imagery shows that a small Central Dense Overcast with cloud tops of -80C is redeveloping over the surface center.

Tropical Storm Gonzalo will be traversing warmer waters, with sea surface temperatures between 29°C and 30°C over the next 24 to 36 hours, allowing for strengthening. Gonzalo has broken the current record for the earliest 7th named storm formation in the Atlantic, edging out Gert on July 24th, 2005.

This tropical storm is forecast to bring adverse weather to the Southern Windwards, including T&T on Saturday into Sunday, with tropical storm and hurricane conditions generally remaining north of T&T.

What We Forecast

Track

North of Tobago, south of Barbados on Saturday 25th July 2020 into Sunday 26th July 2020. This new track is slightly slower than this morning.

Early-cycle track guidance from top models, showing Tropical Storm Gonzalo moving between Trinidad and Barbados as of 00Z Friday 24th July 2020. (NCAR)
Early-cycle track guidance from top models, showing Tropical Storm Gonzalo moving between Trinidad and Barbados as of 00Z Friday 24th July 2020. (NCAR)

Based on present model guidance, the core (i.e. where the heaviest showers and thunderstorms may occur) is forecast to track north of Tobago and south of Barbados on Saturday into Sunday.

Models, and the official forecast, have slightly moved southward and now northward over the last 24 hours.

Given the small radii of circulation, slight track adjustments northward would result in minimal impacts to T&T, while track adjustments southward would mean widespread heavy showers, thunderstorms and gusty winds to the islands.

Zoomed version of the National Hurricane Center’s track for Tropical Storm Gonzalo, as it moves north of Tobago this weekend.

There has been no change in the track forecast reasoning, with Gonzalo expected to accelerate toward the west and west-northwest through the forecast period. The track guidance is fairly tightly clustered, showing Gonzalo’s center crossing somewhere through the Windward Islands between 48-60 hours.

You should not focus on these relatively small shifts in the forecast track from cycle to cycle, and for the Windward Islands, in particular, consider that 48-60 hour forecast points can be off by an average of 60-80 nautical miles. That’s approximately the distance from Toco to Cedros in Trinidad.

The motion of this system continues to be westward, within the stiff mid-tropospheric steering flow provided by an anchored subtropical ridge to the cyclone’s north. The song remains the same, with Gonzalo expected to speed up toward the west and west-northwest through the entire period. The NHC official forecast is based on a blend of the various consensus aids and is down the middle of the tightly clustered guidance.

Intensity

Intensity guidance for Tropical Storm Gonzalo as of 00Z Friday 24th July 2020 (NCAR)
Intensity guidance for Tropical Storm Gonzalo as of 00Z Friday 24th July 2020 (NCAR)

Three days later since Tropical Depression Seven formed, now Tropical Storm Gonzalo and models still continue to grapple with the intensity of this system.

There is still greater-than-normal uncertainty in Gonzalo’s forecast intensity due to its small size and how it will behave in an environment of relatively light shear and warm sea surface temperatures counterbalanced by a lot of dry air.

This morning’s upper air sounding from Barbados revealed a very dry, high statically stable atmosphere with a mean relative humidity of 23 percent and a CAPE of only 327 J/Kg. Consequently, Gonzalo will be moving into a rather harsh thermodynamic environment over the weekend. As a result, the NHC forecast calls for weakening beyond the 48 hour period as it enters the eastern Caribbean sea and dissipation well south of Hispaniola at day 5, or sooner as a few of the global models suggest.

Gonzalo’s small size makes it susceptible to short-term changes in intensity that cannot be reflected in the official forecast.

Hence, a strong tropical storm or borderline Category One hurricane moving north of Tobago, with sustained winds up to 120 KM/H and gusts to 150 KM/H is the likely scenario. There may be slight adjustments to this intensity forecast over the next 36-48 hours, as small systems are difficult to forecast.

In this scenario, Tobago may experience tropical storm conditions, while across Trinidad periphery impacts are more likely. Across Trinidad, wind gusts in excess of 65 KM/H are likely in heavier showers or thunderstorms. Across Tobago, wind gusts in excess of 85 KM/H are expected.

Impacts From Tropical Storm Gonzalo

As we keep reiterating, much of the worst weather associated with this system will remain offshore and north of Trinidad and Tobago, as of Thursday night. The main hazards for Trinidad will be heavy rainfall while Tobago will be both heavy rainfall and gusty winds.

Wind

Across Trinidad, wind gusts in excess of 65 KM/H are likely in heavier showers or thunderstorms. Across Tobago, wind gusts in excess of 85 KM/H are expected with tropical storm conditions possible.

With wind gusts in excess of 85 KM/H, it will be hazardous to be outdoors. Whole trees are expected to be in motion, with tree damage likely. 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, bringing down utility poles and lines. Power outages expected, with damage to trees, power lines and small structures possible.

High Wind Event Precautions
High Wind Event Precautions

Rainfall

Overall rainfall accumulations have remained the same over the three-day period between Friday through Sunday across T&T, but isolated totals may be high. Heavy rainfall will be possible across T&T. Generally, between 25-50 millimeters of rainfall forecast Friday through Sunday, with isolated totals in excess of 100 millimeters in areas of persisting heavy rainfall and thunderstorm activity, mainly across Northern, Eastern Trinidad and Tobago.

There is an elevated threat of street flooding and flash flooding. As of Thursday night, there is a low threat of riverine flooding.

Thunderstorms and Lightning

With thunderstorms, locally severe wind (in excess of 55 KM/H), violent rainfall rates (in excess of 50 millimeters per hour) and lightning are all possible.

Gusty winds and lightning pose a threat to our power grid, causing localized power outages. Lightning may also strike trees, homes, or utility poles, causing damage to property. Lightning can also be deadly to persons outside during a thunderstorm.

Seas and Surf

Seas, mainly on Saturday, forecast to be moderate to rough, with waves up to 3.0 meters, occasionally up to 4.0 meters in open waters. In sheltered areas, up to 1.5 meters and choppy.

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?

Firstly, don’t panic. A tropical storm watch is in effect for Tobago. No alerts are in effect for Trinidad.

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

Given that strongest winds are forecast to remain north of T&T, do not wait until a watch or warning is issued. Though across Tobago, strong wind gusts are the main hazard on that island, across Trinidad, as with most tropical systems moving through our area; our main hazard tends to be heavy, flooding rainfall.

If you live in a flood-prone area, it is always recommended to prepare sandbags and ensure watercourses and guttering on your property are cleared. Secure loose objects outdoors and trim larger trees. You can request assistance from your local city, borough, or regional corporation.

If your roof is not secured, consider securing your roof with hurricane straps. A hurricane strap costs between $8 to $10. It takes about 50 straps to secure the roof of an average three-bedroom house. Most straps are available in your neighborhood hardware and are made with galvanized steel.

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

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