Q COSTARICA -- Tropical Storm Melissa has generated great uncertainty this week. Since Monday, it has rapidly ascended, reaching a 90% chance of formation in just two days, but by Tuesday morning, it had officially become a tropical storm.
However, it has since remained almost stationary in the Caribbean Sea and has not evolved into a hurricane. This combination of rapid origin and minimal movement is raising concerns in the region.
Meanwhile, the national weather service, the Instituto Meteorológico Nacional (IMN), warns that Costa Rica will continue to be under the indirect influence of this system, with increased moisture in the South and Central Pacific.
"Tropical Storm Melissa remains over the Caribbean Sea. The amplitude and slowness of this disturbance are modulating the circulation of the Intertropical Convergence Zone, bringing a slight increase in moisture to the south of the country this Thursday and beyond," reported the IMN.
"There remains some uncertainty regarding the evolution of the tropical storm. The most recent analyses indicate that the country will continue to be under the indirect influence (low to moderate) of this system during the second half of the week, especially in the Central and South Pacific," itadded.
"It looks good, but it isn't"
To better understand the behavior of this system in the Caribbean, Cuban meteorologist José Rubiera offered a precise explanation of what is happening within the system.
"It looks very good, but it isn't. It has strong currents in the upper atmosphere that are pushing all the cloudiness eastward," he noted.
According to Rubiera, the center of circulation is located outside the cloud layer, which means the system's column is tilted.
"As long as it's not vertical, it won't develop," he explained.
Furthermore, there are no currents driving it. Wednesday's analysis indicates it is moving at 1 km/h (0.6 mph), almost stationary.
"This slowness causes the track cone to be practically a circle, with high uncertainty about where it will move," he noted.
Possible Intensification in Warm Waters
Rubiera warned that over the weekend, the wind shear limiting development will diminish.
If the system manages to align vertically and remain over warm waters of 30°C to 31°C (86°F to 88°F), it could intensify rapidly.
"It will literally explode in intensity when it reaches that area, because the heat content of the sea is extremely high," he added.
He also noted that a stronger trough, descending from the southeastern United States, could capture Melissa and deflect it northward or northeastward, increasing the risk for Jamaica, Haiti, and Cuba.
Meanwhile, meteorologist Irina Katchan indicated that on Thursday, Melissa was located approximately 355 km east of Kingston, Jamaica, with maximum sustained winds of 75 km/h (45 mph) and moving northwest at 4 km/h (2.5 mph).
"Melissa is expected to begin intensifying within 48 hours, becoming a hurricane within 48 hours, and a major hurricane within 72 hours, reaching a maximum intensity of 225 km/h (140 mph) within 96 hours," indicated the specialist, who warned of the cyclone's formation in Caribbean waters last week.
If this forecast is confirmed, Melissa would become a Category 4 hurricane.
According to international organizations and experts, the following are expected to evolve into the system in the following hours:
Effect on Costa Rica
Regarding the influence that Melissa may have on Costa Rica in the coming days, the updated IMN report emphasizes an indirect influence.
"The Intertropical Convergence Zone remains active and will be modulated by Melissa throughout the forecast period until Wednesday, October 29," the IMN weekly report states.
"The country will continue to be under the indirect influence of this system, concentrated mainly in the South Pacific, where frequent rains and moderate to heavy downpours are expected," the Meteorological Institute warned.
Also expected are short-lived heavy rains and thunderstorms in the Central Pacific and Central Valley and Occasional downpours in the Northern Zone and the Caribbean, especially over the weekend.
At this time, national experts do not foresee a direct impact from the cyclone on the country, but they do anticipate an increase in humidity that will keep the weather unstable and rainy.