Tropical cyclone tools CKK 2025 / Dvorak / Brown / CKZ / ADT / SCH

Wind ↔ pressure

Estimate cyclone wind and pressure with CKK 2025, Brown, CKZ, or ADT. Convert Dvorak intensity numbers, or use SCH for central pressure estimates from station observations.

CKZ ROCI tutorialWhat to enter, where to find it, and a worked example

CKZ estimates how a cyclone’s maximum wind relates to its central pressure, accounting for its surroundings and structure. Start with an advisory or best-track record for one observation time. Find outer-isobar values in a storm analysis or sea-level pressure chart; the advisory’s central pressure is a different quantity.

Use the calculator in four steps

  1. Choose CKZ and a direction

    Enter a known 1-minute sustained wind at 10 m for Wind → pressure, or a central pressure for Pressure → wind. Both directions use the same ROCI relationship. Use observations from the same time; gusts and 10-minute winds are different inputs.

  2. Set latitude and environmental pressure

    Enter north as positive and south as negative: 20° S becomes −20. The pressure field is Pe, used directly in the equation. The CKZ convention is outermost closed-isobar pressure (POCI) + 2 mb: a POCI of 1008 mb means entering 1010.

  3. Enter the storm’s size

    Enter the radius of the outermost closed isobar (ROCI) from a best-track record or pressure analysis. Use nautical miles, or choose km. This CKZ mode calculates S = ROCI / 480 + 0.1 after converting the radius to nmi; it does not convert ROCI to R34.

  4. Add forward motion and read the result

    Forward speed is how fast the storm’s center moves, in knots. Results update immediately. The pressure deficit is environmental pressure minus central pressure. Open Calculation details to follow the numbers.

References: CKZ paper · Read an NHC advisory

Try it yourself

A KnackBot comparison

The supplied KnackBot CKZ example: 158.8298 kt converts back to 900.0000 mb.

Sustained wind
158.8298 kt
Latitude
20° N
Environmental pressure
1006 mb
ROCI
200 nmi
Forward motion
10 kt
Expected central pressure—

Loading the example replaces the calculator’s inputs. You can restore your previous inputs while this page stays open.

Can I enter R34 instead?

R34 measures the extent of 34-kt winds; ROCI measures the outermost closed pressure contour. They are different radii. For this KnackBot-matched CKZ mode, use an analyzed ROCI rather than entering R34 as ROCI.

Before using a result

Use an analyzed environmental pressure and radius when available. ROCI is a radius, not an eye diameter, RMW, or R34. Keep the same storm inputs when reversing a calculation; rounding a wind value can slightly change the recovered pressure. An estimate from the relationship can differ from an observed storm.

Storm inputs

North + / south −

Pe: outermost closed-isobar pressure + 2 mb for CKZ.

Storm size

TS-force winds start at 34 kt. Average the reported nonzero quadrant radii; enter 0 only when there are no TS-force winds.

Estimated 1-minute wind

CKZ
—mb

Enter the storm inputs to calculate.

Updates as you type

Wind–pressure curve

Same storm inputs
Calculation details

About the methods

CKZ uses the ROCI size rule inferred from the supplied KnackBot results: S = ROCI / 480 + 0.1, with ROCI in nmi. Both Wind → pressure and Pressure → wind use this same relationship, with equation 7a at 18° absolute latitude and under, or equation 7b above 18°. The motion correction is 1.5 × C0.63, where C is in knots. CI → pressure converts CI to wind first. Winds are converted to knots and radii to nmi before calculation.

The supplied KnackBot example gives 900 mb → 158.8298 kt → 900.0000 mb at 20° N, ROCI 200 nmi, forward speed 10 kt, and environmental pressure 1006 mb. The earlier REVCKZ comparisons at ROCI 330, 440 and 600 nmi also match to four decimals. KnackBot’s source and a possible size floor remain unverified. This inferred size rule differs from the published R34 size calculation. Environmental pressure is used directly; when starting from POCI, enter POCI + 2 mb.

CKZ · Original equation only uses the same KnackBot-derived ROCI size rule, S = ROCI / 480 + 0.1, and editable forward speed, but applies the original pressure equation (equation 1 / 7b) at every latitude. It supports both wind–pressure directions and CI → pressure. Its Pressure → wind result matches normal CKZ above 18°; at 18° and under it keeps equation 7b rather than switching to 7a.

CKK · Chavas, Knaff & Klotzbach (2025) predicts central pressure from 1-minute maximum wind, azimuthal-mean R34, latitude, forward speed, and environmental pressure. It uses the final published equation 5 and the author’s motion correction, Vmean = Vmax − 0.55 × forward speed. Winds are converted to m/s and radius to meters internally. For reported quadrant radii, average the nonzero values and choose the × 0.85 convention; if your radius is already an azimuthal mean, choose use directly. ROCI is not an input to this model. Environmental pressure is used as entered; POCI + 2 mb is a proxy when an analyzed environment is unavailable. The model was fitted to aircraft pressure observations in the southwestern North Atlantic and eastern North Pacific during 2004–2022. Pressure → wind numerically inverts the same equation; CI → pressure first converts an existing CI number to wind. The calculator covers 25–250 kt, or at least 34 kt with nonzero R34; this extends beyond the fitting sample.

Dvorak (1984) uses the traditional CI-to-wind and basin pressure tables published by NHC. Enter an existing current intensity (CI) number from 1.0 to 8.0, a 1-minute wind from 25 to 170 kt, or a pressure within the selected table. Intermediate values are linearly interpolated; pressure is unavailable below CI 2.0, and 25 kt corresponds to CI 1.0–1.5. The complete reference table appears in Calculation details. Deriving CI from satellite imagery requires a Dvorak analysis; during weakening, CI can differ from the cloud-pattern T-number.

SCH · Schloemer / Holland pressure profile estimates central pressure from an observed station sea-level pressure, its distance from the center, environmental pressure, and RMW. It solves P(r) = Pc + (Pe − Pc) exp[−(RMW / r)B] for Pc. B = 1 gives the original Schloemer (1954) profile; other B values use Holland’s generalization. The assumed profile is circularly symmetric. Uncertainty in distance, RMW, B, and the station reading affects the estimate, especially far from the center.

Brown, Franklin & Landsea (2006) fitted Atlantic reconnaissance-based best-track observations from 1998–2005. Choose the overall fit or a separate latitude, 12-hour wind-trend, or regional fit. Each uses V = a(b − Pc)c, with V in knots and Pc in mb. The fitted constant b is not an environmental-pressure measurement. The latitude subsets describe north and south of 25° N within the Atlantic sample.

ADT / McIDAS-V reproduces SSEC’s documented CKZ conversion, including its 11-knot motion default and weak-system pressure adjustment. It uses the same relationship in both wind–pressure directions.

All wind results are 1-minute sustained estimates. The CI option starts from an existing intensity number; satellite imagery is needed to derive CI itself. Brown’s equation is inverted algebraically for Wind → pressure; ADT uses a numerical solver for Pressure → wind and can return more than one solution. Brown, CKZ, and ADT cover 25–250 kt; the R34 calculations require at least 34 kt when a TS-force radius is present. This calculation range extends beyond the Brown study’s observations; values below 892 mb, or below 920 mb for its Atlantic sub-basin fit, are extrapolations. These are empirical estimates; real storms can depart from the relationship.

Sources: Chavas, Knaff & Klotzbach (2025)·CKK author’s reference code·Schloemer (1954)·Holland profile equations & evaluation·Brown, Franklin & Landsea (2006)·Courtney & Knaff (2009)·SSEC / McIDAS-V equations & CI table·CIMSS ADT