Tropical Cyclone Norma / Tropical Cyclone 16W (Sanba) / Invest 91A
Wednesday, October 18, 2023

Current Snapshot

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By PDC’s Senior Weather
Specialist Glenn James

The Pacific Disaster Center’s (PDC Global) Wednesday, October 18, 2023, Tropical Cyclone Activity Report…for the Pacific Ocean, the Indian Ocean, and adjacent Seas

Current Tropical Cyclones:

Tropical Cyclone Norma…is located approximately 465 miles south-southeast of Cabo San Lucas, Mexico

Tropical Cyclone 16W (Sanba)…is located approximately 158 NM southeast of Hanoi, Vietnam


Northeast Pacific Ocean:

Tropical Cyclone Norma…


According to the NHC advisory number 6

Norma is moving toward the north near 8 mph (13 km/h). A northward to
north-northwestward motion at a similar forward speed is anticipated for the next couple of days. A slower motion is forecast is expected by the weekend. On the forecast track, Norma could approach the southern portion of Baja California on Saturday.

Maximum sustained winds have increased to near 90 mph (150 km/h) with higher gusts. Additional strengthening is expected tonight. Slight weakening is forecast to begin late this week or over the weekend.

Hurricane-force winds extend outward up to 25 miles (35 km) from the center and tropical-storm-force winds extend outward up to 150 miles (240 km).


SURF: Swells generated by Norma are affecting portions of the coast of southwestern Mexico, and will spread northward along the coast of western Mexico and toward Baja California Sur during the next couple of days. These swells are likely to cause life-threatening surf and rip current conditions.

>>> South of Southern Mexico…

Invest 91E

A weak area of low pressure located several hundred miles south of the Gulf of Tehuantepec is producing a few disorganized showers and thunderstorms. Any development of this system during the next couple of days is expected to be slow to occur. However, environmental conditions are expected to become more favorable for development thereafter, and a tropical depression is likely to form over the weekend or early next week.

The disturbance is forecast to meander for the next several days and then drift northward or northwestward
starting on Sunday or Monday.

* Formation chance through 48 hours…low…20 percent
* Formation chance through 7 days…high…80 percent

Central North Pacific:

There are no tropical cyclones, nor any areas of disturbed weather under investigation by the CPHC at the time of this writing.

Western Pacific, Indian Ocean and adjacent Seas:

Western Pacific

Tropical Cyclone 16W (Sanbu)

According to the JTWC warning number 7

The system had sustained winds of 35 knots, with gusts to 45 knots

Animated satellite imagery shows a medium-sized, developing system that has drifted from the South China Sea into the Gulf of Tonkin just southwest of Hainan and maintained flaring deep convection over the central dense overcast (cdo) and formative bands wrapping tighter from the northeastern periphery into the cdo that is obscuring the low level circulation (llc).

Analysis indicates a marginally favorable environment, with low vertical wind shear and warm sea surface temperatures, and moderate poleward outflow, tempered by the proximity to land.

TS Sanba will track more north-northwestward in the Gulf of Tonkin along the western periphery of a receding ridge to the east. After 36 hours, a secondary ridge approaching from the west will compete for steering, and force the cyclone into a quasi-stationary (qs) mode up to 72 hours before slowly driving it southward.

The marginally favorable environment will fuel a modest intensification to a peak 0f 45 knots by 36 hours. Afterward, land interference from northern Vietnam to the west and Hainan Island to the east, sea surface temperature cooling due to cyclonic upwelling, due to the qs storm motion, then intrusion of cool dry air from China will gradually weaken the system to dissipation in 72 hours.

Arabian Sea

>>> There’s an area of disturbed weather being referred to as Invest 91A…which is located approximately 704 NM east of Socotra

Animated enhanced infrared satellite imagery and a microwave image depict flaring convection to the west and south, wrapping into a gradually consolidating low level circulation center. Another satellite pass shows a slightly oval closed circulation with sparse areas of 15-20 knot winds in the north and south.

Environmental analysis indicates that 91A is in a favorable environment for intensification due to warm sea surface temperatures, low (10-15 knot) vertical wind shear, and good equatorward outflow.