9/25/22 8p Tropical Update: Latest on Tropical Storm Ian from the NHC and model guidance

Here is a look , as of 730p. at Tropical Storm Ian. Don’t be surprised if you wake up tomorrow morning and it is a Hurricane. And perhaps even a strong Category 1 Hurricane, at that.

That blob of red you see int eh middle has popped up during the last 90 minutes. So the overnight latent heat release has already started.

FROM THE NATIONAL HURRICANE CENTER

Here is the latest from the National Hurricane Center…

At 800 PM EDT (0000 UTC), the center of Tropical Storm Ian was located near latitude 17.0 North, longitude 80.8 West. Ian is moving toward the northwest near 12 mph (19 km/h). A turn toward the north-northwest is expected on Monday followed by a northward motion on Tuesday with a slightly slower forward speed. On the forecast track, the center of Ian is expected to pass near or west of the Cayman Islands on Monday, and near or over western Cuba Monday night and early Tuesday. Ian will then emerge over the southeastern Gulf of Mexico on Tuesday.

Maximum sustained winds have increased to near 60 mph (95 km/h) with higher gusts. Additional strengthening is forecast tonight, followed by more rapid strengthening on Monday and Tuesday. Ian is forecast to become a hurricane on Monday and a major hurricane on Tuesday.

Tropical-storm-force winds extend outward up to 35 miles (55 km) from the center.

The minimum central pressure estimated from NOAA Hurricane Hunter aircraft observations is 991 mb (29.26 inches).

NOTABLE HAZARDS

WIND: Hurricane conditions are expected to reach Grand Cayman on Monday, with tropical storm conditions beginning late tonight. Hurricane conditions are expected within the warning area in Cuba by early Tuesday, with tropical storm conditions expected by late Monday.

Tropical storm conditions are expected within the tropical storm warning area in Cuba Monday night and Tuesday. Tropical storm conditions are possible on Little Cayman and Cayman Brac on Monday. Tropical storm conditions are possible in the lower Florida Keys by Tuesday.

RAINFALL: Ian is expected to produce the following rainfall:

Jamaica and the Cayman Islands: 3 to 6 inches, with local maxima up to 8 inches.
Western Cuba: 6 to 10 inches, with local maxima up to 16 inches.
Florida Keys into southern and central Florida Peninsula: 2 to 4 inches, with local maxima up to 6 inches beginning Monday through Wednesday morning.

Heavy rainfall may affect North Florida, the Florida Panhandle and the Southeast Thursday, Friday and Saturday.

These rains may produce flash flooding and mudslides in areas of higher terrain, particularly over Jamaica and Cuba. Flash and urban flooding are possible across the Florida Keys and the Florida peninsula through mid week. Additional flooding and rises on area streams and rivers across northern Florida and parts of the southeast U.S. later this week cannot be ruled out, especially in central Florida given already saturated conditions.

STORM SURGE: The combination of storm surge and the tide will cause normally dry areas near the coast to be flooded by rising waters moving inland from the shoreline. The water could reach the following heights above ground somewhere in the indicated areas if the peak surge occurs at the time of high tide…

East Cape Sable, FL to Card Sound Bridge…1-3 ft
Florida Keys, FL including Dry Tortugas…1-3 ft
Florida Bay…1-3 ft

The deepest water will occur along the immediate coast near and to the right of the center, where the surge will be accompanied by large waves. Surge-related flooding depends on the relative timing of the surge and the tidal cycle, and can vary greatly over short distances. For information specific to your area, please see products issued by your local National Weather Service forecast office.

Storm surge could raise water levels by as much as 9 to 14 feet above normal tide levels along the coast of western Cuba in areas of onshore winds in the hurricane warning area Monday night and early Tuesday.

Storm surge could raise water levels by as much as 2 to 4 feet above normal tide levels along the immediate coast in areas of onshore winds in the Cayman Islands Sunday night into Monday.

SURF: Swells generated by Ian are affecting Jamaica and the Cayman Islands. Swells will spread northwestward to the southwestern coast of Cuba and the coasts of Honduras, Belize, and the Yucatan Peninsula of Mexico on Monday and Monday night. These swells are likely to cause life-threatening surf and rip current conditions. Please consult products from your local weather office.

TECHNICAL DISCUSSION

The organization of Ian has not changed much since this morning. There have been some small bursts of convection closer to the center of the storm this afternoon, but the activity has not yet led to any notable changes in its structure. In fact, the most persistent convection has been in outer rainbands well to the northeast of the circulation near Jamaica.

The SFMR wind data and adjusted flight-level winds from the earlier reconnaissance flights supported surface winds of 35-40 kt, and the initial intensity is set at 40 kt for this advisory. A NOAA Hurricane Hunter aircraft is scheduled to investigate Ian later tonight.

The center of Ian has jogged a bit northward this afternoon, but its longer-term motion is west-northwestward at 300/10 kt. A generally northwestward motion is expected tonight, followed by a
north-northwestward motion on Monday and early Tuesday as it moves across the northwestern Caribbean Sea and near or over western Cuba. From there, the track guidance still diverges at days 3-5 as Ian is forecast to move northward across the eastern Gulf of Mexico.

The ECMWF and UKMET models still lie on the eastern edge of the guidance and bring the center of Ian over the coast of west-central Florida, while the HWRF and HMON models are on the western side of the envelope and show Ian approaching the central Florida panhandle. Notably, the GFS has trended slightly eastward for the past few cycles, which has brought the multi-model consensus aids a bit eastward as well. The latest NHC track forecast has been adjusted in this direction, but only on the order of 15-20 n mi in the extended range. Users are reminded not to focus on the details of the track forecast at longer time ranges, since uncertainty is still high and future adjustments may be required.

Although the storm has yet to develop an inner core, the conditions over the northwestern Caribbean Sea appear very likely to support strengthening once it becomes better organized. Some dry environmental air may have limited convection today, but the GFS- and ECMWF-simulated satellite imagery indicate that deep convection will increase during the diurnal maximum period overnight. Then, significant strengthening is expected with low deep-layer shear and high oceanic heat content along the forecast track. There is still strong support for rapid intensification in the latest intensity guidance, and the NHC intensity forecast shows Ian becoming a hurricane on Monday and a major hurricane on Tuesday.

This forecast remains close to the IVCN multi-model consensus, with some model aids including HCCA showing even higher peak intensities. Strong southwesterly shear develops over Ian by 72 h related to interaction with an upper-level trough, and the structure of the cyclone could significantly degrade before landfall given these hostile conditions. However, Ian is likely to have an expanding wind field
and will be slowing down by that time, which will have the potential to produce significant wind and storm surge impacts across portions of the Florida west coast and the Florida panhandle.

MODEL GUIDANCE

No major changes from the model guidance this afternoon and evening. If anything it slowly drifted back to the east a bit. And the top-end for the forecast data may have come down a touch, too.

Even the SHIPS intensity guidance has eased back from the potential for really gangbusters Rapid Intensification.

THE BOTTOM LINE