ROME — The migrant ships kept sinking. First came a battered, blue-decked vessel that flipped over on Wednesday as terrified migrants plunged into the Mediterranean Sea. The next day, a flimsy craft capsized with hundreds of people aboard. And on Friday, still another boat sank into the deceptively placid waters of the Mediterranean.

Three days and three sunken ships are again confronting Europe with the horrors of its refugee crisis, as desperate people trying to reach the Continent keep dying at sea. At least 700 people from the three boats are believed to have drowned, the United Nations refugee agency announced on Sunday, in one of the deadliest weeks in the Mediterranean in recent memory.

The latest drownings — which would push the death toll for the year to more than 2,000 people — are a reminder of the cruel paradox of the Mediterranean calendar: As summer approaches with blue skies, warm weather and tranquil waters prized by tourists, human trafficking along the North African coastline traditionally kicks into a higher gear.

Taking advantage of calm conditions, smugglers in Libya send out more and more migrants toward Italy, often on unseaworthy vessels. Drowning deaths are inevitable, even as Italian Coast Guard and Navy ships race to answer distress calls. Last year, more than 3,700 migrants died in the Mediterranean, a figure that could be surpassed this year.