Tourism operators have been advised to speed up marketing plans to encourage people to travel domestically and gain from a short-lived tax perk recently approved by the cabinet.
Mr Phuriwat says this time of year is a low period for group travel.
"As the tax measure will last for only two months through June, it is necessary for tour operators to quickly publicise the incentive deals to customers," said Phuriwat Limthavornrat, president of the Association of Domestic Travel.
The cabinet on Tuesday approved a slate of economic stimulus measures, including a tax deduction for spending on tourism services (accommodation and dining) of up to 15,000 baht when travelling to large provinces and up to 20,000 baht in second-tier provinces.
The overall allowance is capped at 20,000 baht. The government expects to lose 1 billion baht in tax revenue.
Mr Phuriwat acknowledged that he was unsure whether the measure would give tourism a strong boost during the rainy season.
"Generally, those who are fond of travelling during this time are individuals, not big groups," he said.
The scheme this time round does not cover expenses by corporations holding seminars or outings, a key difference from last year's tax deduction.
"Many companies prefer organising seminars such as team-building trips during the low season, thanks to good deals from hotels and food restaurants," Mr Phuriwat said.
He held out hope that the next government would extend the measure to last for the entire year, as the full-year scheme in 2018 helped drive domestic travel.
Last year's tax scheme offered individuals and companies a 15,000-baht tax deduction for tourism spending in 55 less-popular provinces.
The Tourism and Sport Ministry reported tourism revenue in second-tier provinces of 266 billion baht in 2018, up from 243 billion baht the year before.
This year, the ministry forecasts 1.12 trillion baht in overall tourism revenue, up 5% from 1.07 trillion in 2018, with the volume of travel rising to 166 million trips from 161 million last year.
Despite the rainy season, Mr Phuriwat said travellers can enjoy nature tourism and greenery at several destinations in Thailand.
"Normally hotels and resorts and even restaurants offer lower prices, and this is a chance for people to plan trips," he said.
Tourists can also enjoy a 15,000-baht tax deduction when buying local products under the One Tambon One Product scheme. Vendors, however, must enter the tax system in order to provide receipts for customers to use in their claims.