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Active Tropical Systems & Formation Outlook
A whole-basin summary of all active tropical cyclones and the NHC
Tropical Weather Outlook, generated with the
tropycal
package. Select a storm below for its official forecast and model guidance.
GEFS ensemble-mean mean-sea-level pressure around the storm (via Herbie) — synoptic-scale context. For ensemble track spaghetti, see the ECMWF ensemble tracks on the General tab.
ZCZC MIATCDEP4 ALL
TTAA00 KNHC DDHHMM
Tropical Depression Four-E Discussion Number 1
NWS National Hurricane Center Miami FL EP042026
200 AM PDT Wed Jul 01 2026
The area of low pressure (95E) over the western East Pacific has
continued to become better organized over the last 12 hours.
Persistent deep convection has developed primarily over the eastern
and southern portions of the circulation, with curved banding
features becoming well defined. Recent scatterometer data
indicate that the system has developed a closed, although somewhat
elongated, low-level circulation with maximum winds around 30 kt.
Subjective Dvorak current intensity estimates have increased to T1.5
from TAFB. Based on these developments, the system has been
designated as Tropical Depression Four-E, with an initial intensity
of 30 kt.
The depression is moving north-northwestward (345/6 kt), and this
general motion is forecast to continue over the next couple of days
along the western periphery of a ridge over the central portion of
the eastern Pacific basin. Models are in fairly good agreement with
this general motion, and the official NHC forecast lies near the
simple and corrected-consensus aids. Towards the end of the period,
as the system weakens and turns westward into the low-level flow,
there is slight timing differences of when that occurs based on the
convective structure. The NHC forecast continues to lie near or
just to the left of the consensus aids towards the end of the
period.
The system has about a day or so to strengthen within a favorable
low-shear, moist environment, supported by upper-level divergence.
The official forecast has the system strengthening into a tropical
storm later today, which is good agreement with the latest intensity
aids. However, as the system moves north-northwestward, it will
encounter cooler SSTs along its track. In about 36–48 hours, wind
shear is forecast to increase, and the system will move into a drier
mid-level airmass. Given the combination of cooler SSTs and the
increasingly unfavorable environment, the system is forecast to
weaken and will eventually struggle to sustain deep convection.
Simulated IR imagery from the GFS and ECMWF suggests the system
could become devoid of deep convection by around 60 hours. Thus, the
NHC forecast calls for the system to weaken into a post-tropical
remnant low at that time, and dissipating into an open trough by
the end of the forecast period.
FORECAST POSITIONS AND MAX WINDS
INIT 01/0900Z 14.5N 126.9W 30 KT 35 MPH
12H 01/1800Z 15.2N 127.0W 35 KT 40 MPH
24H 02/0600Z 16.3N 127.1W 35 KT 40 MPH
36H 02/1800Z 17.4N 127.3W 35 KT 40 MPH
48H 03/0600Z 18.4N 127.8W 30 KT 35 MPH
60H 03/1800Z 19.2N 128.6W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 04/0600Z 19.7N 129.6W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 05/0600Z 20.3N 132.4W 20 KT 25 MPH...POST-TROP/REMNT LOW
120H 06/0600Z...DISSIPATED
$$
Forecaster Kelly
NNNN
HAFS and GEFS guidance is only available for storms in the US/NHC domain (Atlantic & East/Central Pacific). For this system, the basin summary and best-track position are shown.
WDPN31 PGTW 010900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 09W (NINE) WARNING
NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
INITIAL POSITION: 9.2N 163.0E
INITIAL INTENSITY: 30 KTS
GEOGRAPHIC REFERENCE: 1086 NM EAST-SOUTHEAST OF ROTA
MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 07 KTS
SIGNIFICANT WAVE HEIGHT: 12 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
DEPRESSION (TD) 09W AS A QUICKLY CONSOLIDATING SYSTEM WITH LOWER
LEVEL CLOUD BANDS WRAPPING TIGHTLY UNDER A NEWLY DEVELOPING PLUME
OF DEEP CONVECTION THAT APPEARS TO BE THE BEGINNINGS OF A CENTRAL
DENSE OVERCAST. ENVIRONMENTAL ANALYSIS REVEALS A HIGHLY FAVORABLE
ENVIRONMENT, CHARACTERIZED BY LOW (0-5 KTS) VERTICAL WIND SHEAR,
WARM (28-29 C) SEA SURFACE TEMPERATURES, AND STRONG DIVERGENCE
ALOFT FROM A POINT SOURCE OVER THE SYSTEM. THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE BASED ON THE LOWER LEVEL CLOUD LINES
PRESENT IN ANIMATED MSI. THE INITIAL INTENSITY OF 30 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE CIMSS AUTOMATED
INTENSITY ESTIMATED AND AGENCY DVORAK FIXES LISTED BELOW.
INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).
CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) CENTERED TO THE
NORTHEAST
AGENCY DVORAK AND AUTOMATED FIXES:
PGTW: T1.5 - 25 KTS
RJTD: T1.5 - 25 KTS
KNES: T2.0 - 30 KTS
PHFO: T1.5 - 25 KTS
CIMSS ADT: 32 KTS AT 010700Z
CIMSS AIDT: 31 KTS AT 010700Z
CIMSS D-PRINT: 30 KTS AT 010700Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
VWS: 0-5 KTS
SST: 28-29 CELSIUS
OUTFLOW: STRONG POLEWARD
ANALYSIS CONFIDENCE:
INITIAL POSITION: MEDIUM
INITIAL INTENSITY: MEDIUM
INITIAL WIND RADII: NOT APPLICABLE
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: TD 09W WILL CONTINUE TRACKING GENERALLY
NORTHWESTWARD FOR THE NEXT 24 HOURS AS IT REMAINS STEERED BY THE
STR CENTERED TO ITS NORTHEAST. BETWEEN TAU 24-36, A SEPARATE STR
CENTERED TO THE NORTHWEST WILL BUILD AND EXTEND EASTWARD, GAINING
STEERING INFLUENCE OVER 09W IN THE PROCESS. AFTER 09W TRANSITIONS
STEERING RIDGES, IT WILL TRACK EAST-NORTHEASTWARD THROUGH THE
REMAINDER OF THE FORECAST PERIOD. BETWEEN TAU 48-72, THE EASTWARD
EXTENSION OF THE STEERING RIDGE IS EXPECTED TO WEAKEN, CAUSING A
SLIGHT SLOWDOWN IN 09W'S TRANSLATIONAL SPEED. REGARDING INTENSITY,
09W IS CURRENTLY FORECAST TO STEADILY INTENSIFY UNTIL TAU 60. THE
SYSTEM IS EXPECTED TO BRIEFLY INTENSIFY AT A RAPID RATE FROM TAU
60-72 AS IT SLOWS IN THE HIGHLY FAVORABLE ENVIRONMENT. FROM TAU 72
ONWARD, 09W IS EXPECTED TO CONTINUE STEADY INTENSIFICATION. GIVEN
THE HIGHLY FAVORABLE ENVIRONMENT, RAPID INTENSIFICATION (RI) IS
POSSIBLE AS SOON AS TAU 24-48, WITH THE ONLY CURRENT INHIBITOR TO
RI BEING LACK OF ORGANIZATION. ONCE 09W CONSOLIDATES, THE
ENVIRONMENT WILL BE CONDUCIVE FOR UNRESTRICTED INTENSIFICATION.
SHOULD 09W BEGIN SIGNIFICANTLY INTENSIFYING SOONER THAN FORECAST, A
PEAK INTENSITY HIGHER THAN 120 KTS IS POSSIBLE. IN THE LATE-TERM
FORECAST, 09W IS EXPECTED TO ENCOUNTER A DRY AIR MASS TO THE WEST
AND NORTH OF THE SYSTEM; HOWEVER, BY THIS TIME, 09W IS EXPECTED TO
BE A MATURE TYPHOON AND SHOULD BE ABLE TO COCOON ITSELF OFF FROM
THE SURROUNDING DRY AIR, AS INDICATED BY FORECAST MODELS.
ADDITIONALLY, FORECAST MODELS INDICATE 09W WILL HAVE AN EXPANSIVE
WIND FIELD, AND IS EXPECTED TO INTRODUCE DESTRUCTIVE WINDS ACROSS
CNMI AND GUAM AS IT PASSES SOUTH OF TINIAN.
MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THROUGH THE DURATION OF THE FORECAST, WITH THE EXCEPTION
OF NAVGEM AND GFS, WHICH DEPICT A TRACK SIGNIFICANTLY FARTHER
NORTH. EXPERIMENTAL AI MODELS…
HAFS and GEFS guidance is only available for storms in the US/NHC domain (Atlantic & East/Central Pacific). For this system, the basin summary and best-track position are shown.
ECMWF 10-m Streamlines
This map visualizes near-surface winds from the ECMWF operational model using streamlines — continuous curves that show the direction of the wind at every point. Streamlines help us visually detect patterns of atmospheric flow, such as jets, troughs, and areas of rotation.
Forecasters at the NHC monitor 10-meter wind fields for signs of a closed low-level circulation — a common feature of early tropical cyclone formation. When streamlines wrap into a tight, circular pattern and form a closed loop, it may signal that a system is transitioning from a disorganized disturbance into a structured cyclone.
This early organization of wind flow is a key threshold in classifying an area as a potential tropical cyclone. While other ingredients like convection and mid-level humidity are also necessary, closed low-level circulation is often the first structural milestone forecasters look for.
Look for small, circular loops in the streamlines over oceanic regions — especially where other environmental factors also align for storm formation.
ECMWF Predictions
No active storm found in ECMWF data at this time.
Environmental Indicators
Hypothetical TC Drift Paths
This map displays hypothetical tropical cyclone (TC) paths projected from genesis-favorable zones identified by an environmental mask. These paths are computed using the Emanuel Beta and Advection Model, a physically based framework that estimates the motion of nascent cyclones by combining steering-level winds and planetary rotation effects.
The model blends winds from two critical pressure levels — 850 hPa (lower troposphere) and 250 hPa (upper troposphere) — weighted toward the lower level where most of a tropical cyclone's mass resides. It also incorporates a background component associated with beta drift, which arises from the variation of the Coriolis force with latitude.
Each pink trajectory represents a storm initialized from a grid cell where all five environmental thresholds were favorable: high CAPE, low vertical wind shear, high mid-level humidity, warm SSTs, and positive low-level vorticity. Arrows darken with time, tracing the cyclone’s evolution in 6-hour steps. These tracks can move over land given the steering winds, but in reality these storms weaken quickly when no longer over warm water. This means the tracks that move over significant would likely die out quickly and are not well represented in this model.
Hypothetical storms often drift westward and poleward, steered by large-scale tropical flow and Earth's rotation — this helps forecasters anticipate where early-stage disturbances might evolve into organized storms.
Pressure & Rainfall (hPa)
This chart shows 24-hour forecasts of surface pressure (in hPa) and precipitation (in mm) for select U.S. cities.
The data comes from the Open-Meteo API,
which sources its predictions from high-resolution numerical weather models like ICON (from the German Weather Service)
and ECMWF's IFS. These are advanced general circulation models (GCMs) that solve physical equations governing the
atmosphere — including thermodynamics, fluid motion, and radiation — to simulate and forecast future states of weather.
A sudden drop in pressure may signal the approach of a developing storm system. Increasing rainfall intensity often
tracks with tropical activity or frontal systems. These paired indicators help visualize evolving atmospheric instability and potential hazards.
NBDC Gulf Buoy Data
This data comes from the National Data Buoy Center (NDBC), a division of NOAA responsible for monitoring ocean
and atmospheric conditions using moored buoys, coastal stations, and drifting floats. These sensors play a vital role in
tracking tropical cyclone development by recording variables like wind speed,
barometric pressure, air & sea surface temperatures, and wave height — all of which
help determine storm structure and intensification.
A sudden drop in sea-level pressure or a spike in wind gusts can signal rapid cyclone strengthening.
Water temperature above ~26°C is a key fuel source for tropical cyclones. Wave and swell height give insight
into the storm’s reach and energy transfer across the ocean. Monitoring these in real time helps improve forecasts and early warnings.
Wind: NW (310°), 5.8 kt | Gust: 7.8 kt
Pressure: 29.99 steady | Air Temp: 82.4 °F
Water Temp: 85.3 °F | Dew Point: 77.2 °F
Swell: 0.7 ft | Wind Wave: 1.0 ft
NWS U.S. Radar
The National Weather Service (NWS) collects radar data using the NEXRAD (Next Generation Radar) network —
a nationwide system of over 150 high-resolution Doppler radar stations. Radar works by emitting pulses of energy
that bounce off precipitation (like raindrops, hail, or snow) and return to the radar dish. Doppler radar not only detects the
location and intensity of storms, but also their motion — by measuring shifts in frequency caused by movement of particles toward
or away from the radar site. This allows meteorologists to spot rotating storms and potential tornadoes in real time.
GOES 15-min Satellite
The GOES (Geostationary Operational Environmental Satellite) system is operated by NOAA
and provides continuous weather observation over the Americas. Orbiting 22,300 miles above Earth,
GOES satellites deliver high-resolution imagery every 15 minutes, helping track tropical systems, cloud formation,
and atmospheric motion in real time. The Geocolor imagery shown here combines visible and infrared data
to highlight clouds, land, and sea in a natural-looking format.
GOES Band 13 – Infrared (IR) Imagery
Band 13 (10.3 µm) is one of the most important infrared channels for tropical meteorology, measuring emitted radiation from cloud tops.
Colder colors (red, yellow) signal deep convection, where strong thunderstorms punch through the upper atmosphere.
These features often indicate the early stages of tropical cyclone formation.
Most recent GOES Band 13 image. Provided by NOAA/NESDIS/STAR.
