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TheForecast Post

A chronicle of American weather and climate  ·  Wednesday, 16 September 2026

Weather Trader Tropics MILEPOST 738

September 18, 2025 Thursday Hurricane Season

Tropical Storm Gabrielle nearly gave up but is back in business

What the month did

September 2025 was the 7th-warmest September in the 131-year national record (1895–2025), at 67.9°F against a 1991–2020 normal of 66.0°F (+2.0°F).

September 2025 was the 15th-driest September in the 131-year national record (1895–2025), at 1.9in against a 1991–2020 normal of 2.6in (-0.6in).

NOAA/NCEI Climate at a Glance, contiguous United States. This is the observed record for the month, not a score of anything said in this piece — the forecast ledger begins 2026-08-17 and cannot reach earlier posts.

Tropical Storm Gabrielle was a naked swirl of low-level clouds all day but has since erupted with convection down shear — on the eastward side of the center of circulation. Once the shear relaxes and the effects of the mid-level trough (TUTT) subside, then Gabrielle can resume intensifying as an upright, fully functional tropical system.

Temperature Analysis | 6:45 PM ET

HOT in the Mississippi River valley with mid to upper 90s today

Temperature Anomaly | 6:45 PM ET

The heat wave is 15°F to 20°F above normal … and warmth extends from Memphis into the Northeast. Lower 48 is 3.4°F above normal

HRRR Simulated Radar Next 48-hours

North America Precipitable Water | Next 6-days

  1. Next tropical storm in the Eastern Pacific —> (maybe) Narda — will push moisture into Southern California again by this weekend, with another tropical system following as the EPAC blows through the alphabet with weak, short-lived storms.

  2. Tropical Storm Gabrielle passes east of Bermuda but uncertainty about intensity: TS to major hurricane … remains. NHC is at 85-knots (Category 2) maximum

  3. Atmospheric rivers plow into Western Canada and then Pacific Northwest U.S. into next week — autumn like pattern


NWS NDFD Precipitation Next 48-hours

Quite the rainfall for the Sierra and deserts — including Death Valley, Las Vegas, and Phoenix.

NOAA WPC Precipitation + Anomaly | Next 7-days

Little if any rain from the Northeast through Mid-Atlantic into North Florida = brown & red = much below normal through next 7-days.

Tropical moisture into California = huge bonus for the tail end of monsoon season.


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Atlantic Basin Outlook | 5 PM ET Update

1 more area on the Atlantic Outlook but low chance from a tropical wave that just emerged off African coast.

2025 Hurricane Season [Day 110]. My FORECAST for this year is (still) 14 named storms, 7 hurricanes, and 3 major hurricanes (near average)

2025 Season to Date: 7 named storms, 1 hurricanes, and 1 majors | ACE = 41 ACE of Erin: 32.2 (140-knots maximum wind)

Gabrielle should become a hurricane in 4-days by Sunday, but there is uncertainty as the center reformed/jumped northward to almost 20°N … I think previous forecasts of Category 4+ were contingent on a much further south center (15°N) but we may be seeing a reversion to the mean … and NHC going with Category 2.

Tropical Storm Gabrielle (07L) ATCF Spaghetti

ECMWF Ensembles 12z | Gabrielle

Some variety in the maximum intensity but near majority show Category 3 pressure < 960s mb but probably not until it reaches higher latitude — and possibly as a post-tropical cyclone

ECMWF 12-Days Integrated Vapor Transport | 12z cycle

Flagship model ECMWF 12z did not have another wave developing behind Gabrielle

ECMWF 18z | +4 Days MSLP | UV850 | PWAT

Can’t say ECMWF Control (18z) is too terribly interested in Gabrielle with maybe minimal hurricane intensity

HAFS A and HAFS B mesoscale models (18z) with disorganized, minimum TS intensity at Day 5.

The uncertainty with intensity is not unusual with a system in its formative stages … and we have plenty of time to watch Gabrielle as it battles back against dry air and wind shear


Atlantic Satellite Imagery | Infrared

Mid-Level Water Vapor

Tropical Upper Tropospheric Trough (TUTT) undercutting Gabrielle with westerly wind shear and mid-level dry air, but that should subside

SST and SST Anomaly | ECMWF 12:00 UTC Forecast

Warm pool 28° to 29°C plenty sufficient for any category of hurricane along the entire track of Gabrielle (07L)

NOAA Tropical Surface Analysis | 18z

Atlantic Tropical Waves = 3 with the most recent coming off Africa (20%)

Eastern Atlantic and Africa Visible Satellite

The healthy tropical wave that came off Africa today has mostly poofed

Long Loop of IVT from Day 2 to 15

Cool to watch this African easterly wave born in Ethiopia and then take 8-9 days to cross Africa … emerge into the Atlantic at about 15°N — and weaken immediately.


ECMWF EPS 12z Ensemble | All Cyclone Tracks Through 10-days

ECMWF EPS 12z Ensemble | All Cyclone Tracks Through 15-days

Gabrielle might be the ONLY show in town for the next 2-weeks from the full-physics EPS 15-day model


AIFS-ENS Comparison at 12z | Active Tracks at Day 10

AIFS-ENS Comparison at 12z | Active Tracks at Day 15

A.I. trained ensembles are MUCH busier with plenty of tropical cyclones all over the place — but I suspect these are FALSE ALARMS as the AIFS-ENS has been way too eager to develop every tropical wave — likely a bias/problem with the lower resolution (0.25°) model


Eastern Pacific Tropical Update | Invest 96E

Next system would be named Narda but it is running out of time to organize before reaching cooler waters.

Western Pacific Typhoon Season Update | 24W and 25W

3 concurrent tropical storms — and Ragasa and Neoguri should both become powerful Typhoons.

Tropical Storm Ragasa (24W)

The potential intensity of Ragasa is easily Category 5 and could approach T 7.5 (155-knots) in short order heading just north of Luzon, Philippines over some of the deepest and warmest “pool” of tropical SSTs for some of history’s most intense Typhoons.

HAFS-A 12z dips to about 906 hPa

The size of Ragasa will be LARGE but it apparently will fit just between Luzon and Taiwan meaning it will largely head westward into China without disruption. This is not good!

Threat to Hong Kong | ECMWF 18z location on Wednesday

Tropical Storm Neoguri (25W)

HAFS-A with 963 mb central pressure with Neoguri

The parent domain of Neoguri shows a hyper intense Ragasa with 208 knot winds at 850 hPa and a surface pressure of 899 mb … okay then!

EPS 12z Ensemble Spaghetti — Stall and loop in 5-days

ECMWF 18z | 4-days Snapshot | UV850 | PWAT | MSLP

A big Super Typhoon + a little Super Typhoon = 2 maybe!

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Milepost
738 · laid 2025-09-19T00:22:30.052000Z
Source
https://weather.substack.com/p/september-18-2025-thursday-hurricane
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6f300fce937b4b666406066a1065ebd92c01ca42163db833a45810759757be4b
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