Nothing heralds the arrival of the summer auctions quite like a vibrant seaside scene — be it in the hand of Claude Monet, Lyonel Feininger, or even René Magritte. Both Sotheby’s and Christie’s are holding significant Impressionist and Modern evening sales in London this week, a far cry from the days when the auction market would traditionally cool down for the season. “We’re seeing a very strong market for top quality Impressionist paintings this summer,” the vice chairman of Impressionist & Modern Art Worldwide at Sotheby’s, Helena Newman, said.

On Wednesday, Sotheby’s will put up Monet’s “La Plage à Trouville” and the house expects the masterpiece to fetch between $13.89 million and $19.84 million. The Monet beach scene is among Ms. Newman’s favorites in the 56 lots. “It’s an iconic work,” she said. “Monet was exploring the effects of the wind and the light on the water, all quintessentially Impressionist effects.”

Monet completed his painting in 1870 while vacationing with his wife and son at the tony French resort town of Trouville. In fact, the artist so enjoyed his summer stay that he painted another beach scene of the same name. That version of “La Plage à Trouville” hangs in the Wadsworth Atheneum in Hartford, Conn., a two-hour drive from New York City.

Another notable lot in the Sotheby’s sale is the Italian Futurist Gino Severini’s “Danseuse,” painted after the artist had visited Paris in 1915 and seen the latest works of Picasso. “It’s very rare,” Ms. Newman said. “We last sold a Severini in 1990 in New York City for $3.6 million.”

Like the Monet beach scene, Sotheby’s places an estimate of between $13.89 million and $19.84 million on “Danseuse.”

Ms. Newman said that two of the most popular lots among potential buyers at the London exhibitions are a sculpture and a painting by Alberto Giacometti. His oil-on-canvas “Tête Noire (Diego)” could sell for between $5.96 million and $7.94 million.

Giacometti’s bronze sculpture “Trois Hommes Qui Marchent 1” is expected to fetch between $7.94 million and $11.91 million. “The three men walking is just fabulous,” Ms. Newman said.

Christie’s Impressionist and Modern sale promises to be another blockbuster evening. Tuesday’s auction in London is led by the private collection of the Indiana industrialist J. Irwin Miller and includes Claude Monet’s “Le bassin aux nymphéas,” which Christie’s estimates could sell for between $36 million and $47 million.

“Monet was a perfectionist at this point in his career and it shows in this painting,” a Christie’s spokesman, Matthew Paton, said. “I can’t think of any other Impressionist sale in London with this kind of Monet.”

The 1919 oil on canvas is one of the largest and last water-lilies scenes painted by Monet. For the last four decades it hung over a concert grand piano in the living room of Miller, the late longtime head of the Cummins Engine Co. and a noted patron of Modern art and architecture.

The Millers lived in a house designed by their friend, the architect Eero Saarinen, and filled it with Impressionist and Modern works during the latter half of the 20th century. The collection includes “La pudeur (L’italienne)” by Henri Matisse, an oil on panel that dates to 1906. Christie’s estimates the work could sell for between $6 million and $7.9 million. “It’s absolutely beautiful,” Mr. Paton said.

One of Miller’s favorite paintings was “Compotier et guitare” by Pablo Picasso. The large oil on canvas hung in a prominent position in the Miller family’s dining room, a logical place for a composition that includes a bowl of fruit and wine. Christie’s places an estimate of between $6 million and $7.9 million on the painting.

A work of Edgar Degas up for auction at Christie’s has an interesting New York City provenance. The artist’s pastel, gouache, and charcoal on paper, “Danseuses à la barre,” was completed in 1880 and for the next 100 years remained part of the collection of H.O. Havemeyer and his heirs.

The Havemeyers left their collection to the Metropolitan Museum of Art decades ago, with the exception of a few works, among them “Danseuses à la barre.” “That the Havemeyers kept it in the family is a testament of just how special this Degas is,” Mr. Paton said.

Christie’s places an estimate of between $7.9 million and $12 million on the picture, one of 81 lots in tomorrow’s evening sale.