1. Marco is forecast to strengthen to a hurricane as it moves intothe southeastern Gulf of Mexico by tonight, and tropical stormconditions are expected over the northeastern coast of the YucatanPeninsula and in extreme western Cuba. Heavy rainfall is alsoexpected in the eastern portions of the Mexican states of QuintanaRoo and Yucatan, and across far western Cuba, which could result inflash flooding.

2. Marco is expected to move across the central Gulf of Mexico as ahurricane Sunday and approach the central Gulf Coast on Monday.There is an increasing risk of impacts from storm surge, winds, andheavy rainfall from the upper Texas coast to Louisiana early nextweek, and interests there should monitor the progress of Marco, asstorm surge, tropical storm, and/or hurricane watches could beissued later today.

CHANGES WITH THIS ADVISORY:

None.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT:

A Tropical Storm Warning is in effect for...
- Province of Pinar del Rio Cuba
- Cancun to Dzilam Mexico

A Tropical Storm Warning means that tropical storm conditions are expected somewhere within the warning area, in this case within the next 612 hours.

Interests along the coasts of Louisiana and Texas should monitor the progress of Marco. Watches will likely be required for a portion of this area later today.

For storm information specific to your area, please monitor products issued by your national meteorological service.

WIND: Tropical storm conditions are expected within the warning area in Cuba through this afternoon. Tropical storm conditions are also still possible today within the warning area along the northeastern coast of the Yucatan Peninsula of Mexico.

RAINFALL: Marco is expected to produce 1 to 4 inches of rain, with isolated maximum amounts of 6 inches possible, across the eastern portions of the Mexican states of Quintana Roo and Yucatan, and across far western Cuba. This rainfall may result in areas of flash flooding.

At 100 PM CDT (1800 UTC), the center of Tropical Storm Marco was located near latitude 21.4 North, longitude 85.5 West. Marco is moving toward the northnorthwest near 12 mph (19 km/h), and this general motion is expected to continue through Sunday morning. A gradual turn toward the northwest and westnorthwest is expected to begin Sunday afternoon and continue through Tuesday morning. On the forecast track, Marco's center will move into the southeastern Gulf of Mexico by this evening. Marco will then move across the central Gulf of Mexico on Sunday and approach the central and northwestern Gulf coast on Monday and Tuesday.

Maximum sustained winds are near 65 mph (100 km/h) with higher gusts. Strengthening is forecast during the next day or two, and Marco is expected to become a hurricane later today or tonight. Weakening is forecast to occur on Monday and Tuesday.

Tropicalstormforce winds extend outward up to 45 miles (75 km) from the center.

The estimated minimum central pressure is 992 mb (29.30 inches).

Reconnaissance data, geostationary and microwave satellite imagery,and radar data from Cuba all indicate that Marco is strengtheningquickly this morning. The Air Force Reserve Hurricane Huntersmeasured a peak 850-mb flight-level wind of 69 kt, and there wereseveral SFMR measurements of 50-55 kt to the northeast of thecenter. These data support raising Marco's initial intensity to 55kt, and the central pressure based on dropsonde data has fallen to992 mb. The crew on the plane reported the formation of a partialeyewall, which agrees with what we've seen on recent microwave andradar images.

The track forecast has been complicated by the fact that the planehas fixed Marco's center to the east of the previous forecasttrack, and that makes the current motion north-northwestward, or340/10 kt. The subtropical ridge currently located over thesouthwestern Atlantic is forecast to build westward along thenorthern Gulf Coast during the next few days, and this expandingridge is expected to push Marco northwestward and then eventuallywestward while the cyclone moves across the Gulf of Mexico. Thisgeneral thinking has not changed, but the adjusted initial positionended up shifting the track guidance to the north and east on thiscycle. In response, the new NHC track forecast has been adjustedeastward and northward during the first 3 days and is generallybetween the HCCA and TVCN consensus aids.

Marco has finally tapped into the favorable conditions over thenorthwestern Caribbean Sea, and the cyclone's overall small size andsmall radius of maximum winds makes it susceptible to quick changesin intensity. The tropical storm is just beginning to move into ahigher zone of shear to its north, but conditions should remainconducive enough for Marco to intensity to a hurricane during thenext 24 hours. After that time, southwesterly shear is expected toincrease over 20 kt by day 2 and then over 30 kt by day 3, and thoseconditions, along with the cyclone's small size, should causeweakening as Marco gets closer to the central and northwestern Gulfcoast. The updated NHC intensity forecast has been increased duringthe first 2 days and lies above the HCCA/Florida StateSuperensemble solutions but below the SHIPS/LGEM scenarios. Theintensity forecast comes back in line with the previous forecast byday 3 during the expected weakening phase, and Marco is ultimatelyexpected to dissipate over Texas by the end of the forecast period.

The updated track forecast suggests that watches could be requiredfor a portion of the central Gulf Coast later today.