Moody's Analytics expects Thai gross domestic product (GDP) growth of 4.1% for the second quarter, while local economists are offering a dismal 2.5% forecast due to lacklustre domestic demand, declining investment and weak exports.
"The Thai economy has hit a major speed bump," Moody's Analytics said in a report.
"Monthly household consumption, export and production data suggest the economy expanded by 4.1% year-on-year in the second quarter, down from 5.3% recorded a quarter before."
Moody's Analytics forecasts full-year economic growth of 4.3%, a touch below potential growth of 4.5%.
The Thai economy is expected to perform at potential next year as the improving global economy lifts export industries, according to Moody's Analytics.
The Bank of Thailand and the Fiscal Policy Office (FPO) recently said economic growth in the second quarter could come in below 4%.
The central bank last month trimmed its 2013 GDP growth forecast to 4.2% from 5.1%, while both the National Economic and Social Development Board (NESDB) and the FPO earlier said economic growth could come in at 4% this year.
The NESDB, a government think tank, will release second-quarter GDP figures on Aug 19.
Moody's Analytics expects monetary policy will remain accommodative through the rest of this year but believes the Bank of Thailand will be reluctant to cut rates further on uncertainty about US stimulus curbs.
"The central bank will also be wary of stoking demand for loans, which remains heated despite softer consumer loan growth in the opening quarter of 2013," the firm said.
Moody's Analytics warns a hard landing in the Chinese economy could shave 1.3 percentage points off GDP growth, with export industries bearing the brunt of the slowdown.
Kampon Adireksombat, the head of Tisco Securities' economic strategy unit, said his house predicts the economy will expand by a mere 2.5% in the second quarter due to the slowdown in domestic demand and investment plus shrinking exports.
The figure does not imply a dismal growth outlook for the Thai economy but rather is a function of normalisation since the government's stimulus measures ended last year, he said, adding that full-year growth of the Thai economy is still projected at 4.5%.
He said if approved, the 2-trillion-baht megaproject bill should drive the economy and lead to a "crowding-in" effect for private investment.