Tropical storm warnings were in effect for the southern and northern coasts of the Dominican Republic and the southern coast of Haiti on Wednesday, as Tropical Storm Franklin threatened to bring heavy rainfall and potentially life-threatening flash flooding to the countries’ shared island of Hispaniola, meteorologists said.

As of 5 a.m. on Wednesday, Franklin was about 118 miles southwest of Santo Domingo, the capital of the Dominican Republic. The storm had maximum sustained winds of about 50 miles per hour and was moving north at 10 m.p.h., according to the National Hurricane Center.

The center of the storm was expected to slowly drift and reach the southern coast of Hispaniola early Wednesday and cross the island throughout the day before emerging over the southwestern Atlantic Ocean by Wednesday evening.

The tourism office of the Dominican Republic announced on Tuesday that three of the country’s international airports would close from 10 p.m. local time until 6 a.m. on Wednesday, and two others would cease operations at midnight.

The Turks and Caicos were under a tropical storm warning. A tropical storm warning means that tropical storm conditions are expected somewhere within the warning area within 36 hours. A watch extends that time window to within 48 hours.

Parts of Hispaniola were expected to receive between five and 10 inches of rain, with isolated totals up to 15 inches. Farther east, Puerto Rico could receive up to six inches of rain through the middle of the week, the Hurricane Center said. This amount of heavy rainfall may produce areas of flash and urban flooding as well as river rises and mudslides.

Strong and variable winds at higher altitudes have kept this storm disorganized and prevented it from strengthening into a hurricane. The storm could weaken further when it interacts with the rugged terrain of Hispaniola. However, once it crosses the island and re-emerges over the Atlantic, it is expected to strengthen, likely becoming a hurricane this weekend.

Franklin is the Atlantic hurricane season’s fourth named storm to form in two days. Tropical Storm Emily was downgraded on Monday to a post-tropical cyclone after forming the day before, and Gert was also short-lived. Tropical Storm Harold formed early Tuesday in the Gulf of Mexico and made landfall in Texas in the morning.

Franklin is the seventh tropical cyclone to reach tropical storm strength this year.

The Hurricane Center announced in May that it had reassessed a storm that had formed off the northeastern United States in mid-January, determining that it was a subtropical storm and thus making it the Atlantic’s first cyclone of the year.

The Atlantic hurricane season started on June 1 and runs through Nov. 30.

In late May, the National Oceanic and Atmospheric Administration predicted that there would be 12 to 17 named storms this year, a “near-normal” amount, forecasters said. On Aug. 10, NOAA officials increased its estimate to 14 to 21 storms.

There were 14 named storms last year, coming on the heels of two extremely busy Atlantic hurricane seasons in which forecasters ran out of names and had to resort to backup lists. (There were a record 30 named storms in 2020.)

This year features an El Niño pattern, which started in June. The intermittent climate phenomenon can have wide-ranging effects on weather around the world, and it typically impedes the number of Atlantic hurricanes.

In the Atlantic, El Niño increases the amount of wind shear, or the change in wind speed and direction from the ocean or land surface into the atmosphere. Hurricanes need a calm environment to form, and the instability caused by increased wind shear makes those conditions less likely.

(El Niño has the opposite effect in the Pacific, reducing the amount of wind shear.)

At the same time, this year’s heightened sea surface temperatures pose a number of threats, including the ability to supercharge storms.

That unusual confluence of factors has made making storm predictions more difficult.

“Stuff just doesn’t feel right,” Philip Klotzbach, a researcher at Colorado State University who studies hurricanes, said after NOAA released its updated forecast in August. “There’s just a lot of kind of screwy things that we haven’t seen before.”

There is consensus among scientists that hurricanes are becoming more powerful because of climate change. Although there might not be more named storms overall, the likelihood of major hurricanes is increasing.

Climate change is also affecting the amount of rain that storms can produce.

In a warming world, the air can hold more moisture, which means that a named storm can hold and produce more rainfall, as Hurricane Harvey did in Texas in 2017, when some areas received more than 40 inches of rain in less than 48 hours.

Researchers have also found that over the past few decades storms have slowed, sitting over areas for longer.

When a storm slows over water, the amount of moisture the storm can absorb increases.

When a storm slows over land, the amount of rain that falls over a single location increases; in 2019, for example, Hurricane Dorian slowed to a crawl over the northwestern Bahamas, resulting in a total rainfall of 22.84 inches in Hope Town during the storm.

Other potential effects of climate change include greater storm surges, rapid intensification and a broader reach of tropical systems.

Christopher Mele, Eduardo Medina Chris Stanford, Hogla Enecia Pérez, and Lauren McCarthy contributed reporting.