A quick-hitting but intense surge of heat for this time of year is expanding across the South and will peak Wednesday into Thursday. Numerous records for warmth are anticipated from Texas to Florida and northward into the Mid-Atlantic.

Temperatures — up to 10 to 20 degrees above normal — will feel more like midsummer than early May.

Already, temperatures surpassed 105 degrees near the Rio Grande in the southernmost parts of Texas on Monday and Tuesday. Heat indexes — a measure of how hot it feels after factoring in humidity — soared to 110.

Records fell in the swelling hot-air mass. Widespread afternoon highs above 90 are forecast for several days across much of the Gulf Coast, while highs of 105 to 110 may continue scorching southern areas of Texas. Heat indexes could rise above 115 in the most stifling locations.

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“Those spending a prolonged period outside will need to take necessary heat precautions to avoid heat-related illnesses,” wrote the National Weather Service office serving Brownsville, Tex., and its surrounding area.

The newly operational HeatRisk product from the Weather Service and Centers for Disease Control and Prevention indicates moderate to major (Level 2 or 3 out of 4) health effects from excessive heat through Friday from Texas to the northern Gulf Coast and Florida. Locations near Brownsville, where a heat advisory is in effect Wednesday, may see “extreme” (or Level 4) heat risk at times.

Unseasonable warmth began swelling northward Monday. Several record-warm nighttime lows were established Monday along the Gulf Coast and into the Southeast, including in Corpus Christi, Tex., and Charlotte. The number of records is projected to increase Tuesday and Wednesday.

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Although this bout of heat is unusual for early May, it should be mercifully short-lived.

How hot will it get?

Temperatures turn hotter and cover a larger area Wednesday.

Heat in the 90s will expand northward over parts of the South and into the southeastern Mid-Atlantic near Richmond and Norfolk, perhaps creeping as far north as Washington. Record-challenging mid-90s are possible in Jacksonville and Charleston, with low 90s around Houston, Dallas and New Orleans. Areas of far southern Texas will probably rise past 105 for a third-straight day. Heat indexes could exceed 100 in much of east and Southeast Texas, and up to 115 in the far south.

More than a dozen record highs will probably be set. Del Rio, Tex., is forecast to reach 105, which would beat the existing high of 103 in 1967. Other cities where records could fall include Montgomery, Ala. (forecast high of 92); Wilmington, N.C. (92); and Richmond (91).

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As many as 50 to 100 record-warm lows could be set, from southern parts of Texas to the Florida Keys and then north through the Mid-Atlantic.

Thursday will probably be as hot as Wednesday in many areas, although the northern extent will shrink.

Highs in the 90s will probably be widespread in the eastern Carolinas, southern Georgia, Florida, then westward through Houston. Areas of far southern Texas, especially around the Rio Grande, will again see highs near or surpassing 100.

Somewhat fewer places could set record highs compared to Wednesday, but Laredo (forecast high of 108) and Brownsville (101) in Texas, New Orleans (92), and Daytona (94) could see new high marks. Heat indexes close to 100 should stretch from southeastern Texas across the northern Gulf Coast and into Florida, with 115 again likely in far southern Texas.

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Dozens of additional record-warm lows could be set from Virginia to the northern Gulf Coast and Florida, including Key West, where a run of morning lows of 80 degrees or higher is likely.

Friday and Saturday

Relief from the heat is predicted heading into the weekend.

Florida, however, will be an exception, where highs in the low and mid-90s may linger, as a cold front remains to its north Friday. Record highs are possible over most of the peninsula before the potential for records retreats toward South Florida and the Keys by Saturday as the front pushes south.

How hot has it been?

Temperatures rose as high as 105 in Rio Grande Village, Tex., on Tuesday, following a high of 107 on Monday.

A heat index of 109 was observed in Brownsville, where highs in the mid-90s mixed with oppressive humidity as dew points soared into the mid- and upper 70s. Corpus Christi spent much of the day with heat indexes around 100, despite highs in the mid-80s, and heat indexes in the mid-90s arrived in Houston.

Record highs included 88 in Batesville, Ark., surpassing 87 in 1940. Farther east, Lakeland, Fla., (94) and Newport, N.C., (86) also set record highs.

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Record-warm lows were much more numerous, stretching from the Texas-Mexico border to Southern New England. In the Mid-Atlantic, Washington’s morning low of 68 was the highest for the date. Other cities that set record-warm lows include Bridgeport, Conn. (56); Huntington, W.Va. (65); Huntsville, Ala. (69); New Orleans (78); and Brownsville (80).

Looking ahead

The cold front responsible for whisking away the heat is predicted to push deep into the Gulf of Mexico and into the Florida Keys before stalling out by Monday.

But relief from the heat may not last long — maybe just five or so days. Warmer-than-normal waters in the Gulf of Mexico and a change in the weather pattern should support a return of the heat later next week.

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