June 24 (Reuters) - Online spending among shoppers on the first day of Amazon's Prime Day rose 5.3% from a year earlier to $8.3 billion across U.S. retailers, Adobe Analytics said on Wednesday.

The four-day shopping event, which started on Tuesday and is being held earlier than usual this year, will be a litmus test of U.S. shoppers' spending power as the focus shifts to essential goods.

Here are some key details:

• Online spending on Tuesday is tracking ahead of its projections and marks the biggest e-commerce day so far in 2026, Adobe said.

• The data firm reaffirmed its forecast of U.S. retailers driving $26.3 billion in online spend through the event.

• Adobe said sales were driven by categories such as electronics and appliances, tools and home improvement, but purchases of everyday essentials also ticked up.

• Discounts are expected to remain in the 10% to 24% band seen on the first day, Adobe said.

• Adobe's forecast is based on an analysis of 1 trillion visits to U.S. retail e-commerce sites, covering 100 million stock keeping units and 18 product categories.