Tropical Storm Gonzalo Has An Uncertain Future, Track Shifted Southward

Tropical Storm Gonzalo Key Messages:
– Watches & Warnings: A Hurricane Watch is in effect for Barbados, St. Vincent and the Grenadines. Additional watches and warnings may be issued this afternoon for the Southern Windwards.
– Track: Tropical Storm Gonzalo is forecast to move across the region on Saturday, with the track of the system now moving just north of Tobago.
– Intensity: There is great uncertainty 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 130 KM/H and gusts to 160 KM/H. Across T&T, wind gusts in excess of 65 KM/H are likely in heavier showers or thunderstorms.

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

Rainfall: As of Thursday morning, 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. There is an elevated threat of street flooding and flash flooding as showers and thunderstorms associated with tropical systems can produce violent rainfall rates. As of Thursday morning, there is a low to moderate threat of riverine flooding.
– 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.

NHC: Tropical Storm Gonzalo to Strengthen Into A Hurricane On Thursday

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

The National Hurricane Center, as of 11:00 AM, continues to issue advisories on Tropical Storm Gonzalo, 1,485 KM east of the Windward Islands.

At 11:00 AM AST, the center of Tropical Storm Gonzalo was located near latitude 9.6 North, longitude 48.3 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 Saturday evening.

Maximum sustained winds are near 65 MPH (100 KM/H) with higher gusts. Some strengthening is forecast during the next couple of days, and Gonzalo could become a hurricane tonight or on Friday.

Gonzalo is a small storm, and tropical-storm-force winds extend outward up to 35 miles (55 KM) from the center. The estimated minimum central pressure is 997 millibars.

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 conditions are possible within the watch area by Saturday afternoon, with tropical storm conditions possible by midday 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.
Tropical Storm Gonzalo Watches & Warnings as of 11:00 AM Thursday 23rd July 2020.

A Hurricane Watch is in effect for Barbados and St. Vincent and the Grenadines.

This means that hurricane conditions (sustained winds of 74 MPH or greater) are possible within your area. Because it may not be safe to prepare for a hurricane once winds reach tropical storm force, The NHC issues hurricane watches 48 hours before it anticipates tropical storm-force winds.

There are no alerts, watches, or warnings in effect for the remainder of the Southern Windwards as of 11:00 PM Thursday 23rd July 2020.

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 morning (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. Recently-obtained GCOM and WindSat microwave data from overnight show that Gonzalo’s center is a little farther south than previously estimated. In addition, the storm’s structure has become a little disheveled since yesterday, with the deep convection losing some organization. SAB’s data-T number responded to this by falling to 2.5, but overall the CI numbers and SATCON support maintaining 55 kt for now.

Tropical Storm Gonzalo will be traversing warmer waters, with sea surface temperatures between 29°C and 30°C over the next 24 to 48 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, with tropical storm and hurricane conditions generally remaining north of T&T.

What We Forecast

Track

Just North of Tobago, south of Barbados on Saturday 25th July 2020.

Early-cycle track guidance from top models, showing Tropical Storm Gonzalo moving between Trinidad and Barbados as of 12Z Thursday 23rd July 2020. (NCAR)
Early-cycle track guidance from top models, showing Tropical Storm Gonzalo moving between Trinidad and Barbados as of 12Z Thursday 23rd July 2020. (NCAR)

Based on present model guidance, the core (i.e. where the heaviest showers and thunderstorms may occur) is forecast to track just north of Tobago and south of Barbados on Saturday. Models over the last 12 hours continue to trend southward.

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

Even with the southward adjustment of the initial position, Gonzalo still appears to be moving westward, or 270/12 kt. The subtropical ridge to the north is forecast to push Gonzalo toward the west or west-northwest, with an increase in forward speed, for the entire 5-day forecast period. Much of the track uncertainty hinges on exactly how strong Gonzalo gets, with the stronger model representations showing the storm making more poleward process.

Models such as the ECMWF and UKMET, which keep Gonzalo weak or open it up into a trough, are along the southern side of the guidance envelope. The updated NHC track forecast has been shifted southward some, to account for the new initial position and to be a little closer to the intensity consensus, HCCA, and the Florida State Superensemble.

Intensity

Scenario 1: A well-organized tropical storm/borderline Category 1 Hurricane north of Tobago – the current NHC forecast

Intensity guidance for Tropical Storm Gonzalo as of 12Z Thursday 23rd July 2020 (NCAR)
Intensity guidance for Tropical Storm Gonzalo as of 12Z Thursday 23rd 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 an incredible amount of uncertainty in Gonzalo’s intensity forecast. Sea surface temperatures to the east of the Windward Islands are warm–close to 29C–and the storm is likely to be moving through an environment of relatively light shear at least for the next 48 hours or so.

The ambient environment is not particularly moist, however, with mid-level relative humidity generally around 50 percent, and it already appears that this dry air is affecting Gonzalo. Small cyclones like Gonzalo tend to succumb to any type of adverse environmental conditions quite easily, and it’s possible that the system could struggle during the next couple of days. This is the solution shown by some of the global models, particularly the ECMWF and UKMET.

On the other hand, the hurricane statistical and dynamical models, as well as the GFS, continue to show Gonzalo strengthening to a hurricane before it reaches the Windward Islands. Out of an abundance of caution, the official forecast continues to show Gonzalo becoming a hurricane in about 24 hours, but the uncertainty in this scenario cannot be stressed enough. There is a higher degree of certainty that Gonzalo would weaken once it moves over the eastern and central Caribbean Sea, where even the GFS shows it opening up into a wave.

Hence, a strong tropical storm or borderline Category One hurricane moving north of Tobago, with sustained winds up to 130 KM/H and gusts to 160 KM/H is the likely scenario. There may be slight adjustments to this intensity forecast over the next 1-2 days, as small systems are difficult to forecast.

In this scenario, Tobago may experience tropical storm or hurricane conditions, while across Trinidad tropical storm conditions are possible, wind gusts in excess of 65 KM/H are likely, particularly near showers and thunderstorms.

Scenario 2 (still unlikely): Gonzalo rapidly intensifies into a hurricane, moving slower and across the French Antilles.

Statistical-dynamical models and some of the hurricane regional models showing the system becoming a hurricane within the next few days. With compact systems like Tropical Storm Gonzalo, these outcomes are possible.

Generally, the stronger (intensity) a tropical cyclone is east of the Lesser Antilles, the further north it recurves. This intensity depends on how much organization the storm can attain over the next 24 hours. The SHIPS model does show above average indicators for rapid intensification.

As mentioned, just north of Tropical Storm Gonzalo, a surge of trade winds and dry Saharan air will serve as a detriment to the cyclone,.

In this scenario, little to no impacts are expected across T&T. In fact, winds may calm across the islands, allowing for near-record high temperatures with locally heavy showers and thunderstorms possible – but due to localized climatic features.

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 morning, Given the southward adjustment of the track, adverse impacts are becoming increasingly likely for T&T.

Wind

Tobago may experience tropical storm or hurricane conditions, while across Trinidad tropical storm conditions are possible, wind gusts in excess of 65 KM/H are likely, particularly near showers and thunderstorms.

With wind gusts in excess of 65 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, bringing down utility poles and lines. Localized power outages expected.

High Wind Event Precautions
High Wind Event Precautions

Rainfall

Overall rainfall accumulations have increased 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 morning, there is a low to moderate 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. No alerts (as of Thursday morning) are in effect by the Trinidad and Tobago Meteorological Service.

An important note: if this system organizes further, tropical storm watches or warnings may be issued for parts of the Southern Windwards later this week. Regardless of if a warning is issued or not, be prepared.

Secondly, 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.

Tropical Storm Gonzalo is still one to two days away, so a lot can change. Tropical storm watches may be issued 48 hours in advance if tropical-storm-force winds are possible, while tropical storm warnings would be issued 36 hours ahead of expected tropical-storm-force winds. Given that strongest winds are forecast to remain north of T&T, do not wait until a watch or warning is issued. You should continue to monitor updates from official and trusted sources.

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 neighbourhood 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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