TY 09W(SAOLA) skirting Hong Kong within 24h//TY 10W(HAIKUI) to strike TAIWAN after 48h//TS 11W(KIROGI)//3 week GTHO maps//0103utc

JTWC IS ISSUING 6HOURLY WARNINGS AND 3HOURLY SATELLITE BULLETINS ON 09W(SAOLA), 10W(HAIKUI) AND 11W(KIROGI).

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: AS REVEALED IN ANIMATED RADAR IMAGERY, TYPHOON (TY) 09W HAS COMMENCED ANOTHER EYEWALL REPLACEMENT CYCLE (ERC) WITH A SMALL INNER EYEWALL SURROUNDED BY A MOAT AND DEVELOPING OUTER EYEWALL. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A 17 NM ROUND EYE WITH TIGHTLY CURVED SPIRAL BANDING, WHICH SUPPORTS THE INITIAL POSITION WITH HIGH CONFIDENCE. OVERALL, ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE AS THE SYSTEM SLOWLY APPROACHES HONG KONG WITH RADIAL OUTFLOW AND AN ENHANCED POLEWARD OUTFLOW CHANNEL INTO THE WESTERLIES TO THE NORTH. THE INITIAL INTENSITY OF 120 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON DVORAK INTENSITY ESTIMATES RANGING FROM 6.0 TO 6.5, A 010000Z AIDT ESTIMATE OF 121 KNOTS, AND AN RCM-3 SAR VMAX OF 116 KNOTS. THE WIND RADII HAVE BEEN EXPANDED BASED ON THE RCM-3 SAR PASS WITH HIGH CONFIDENCE.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TY 09W IS FORECAST TO TRACK WEST-NORTHWESTWARD TO WESTWARD ALONG THE SOUTHERN PERIPHERY OF THE STR THROUGH TAU 24. AFTER TAU 24, THE SYSTEM WILL TRANSITION TO THE STEERING INFLUENCE OF A BROAD WESTERN STR, WHICH WILL DRIVE THE SYSTEM WEST-SOUTHWESTWARD TO SOUTHWARD THROUGH TAU 72. TY 09W WILL WEAKEN STEADILY DUE TO FRICTIONAL EFFECTS AND DRY AIR ENTRAINMENT AS IT SKIRTS THE SOUTHEAST COAST OF CHINA. THE ONGOING ERC WILL ALSO CONTRIBUTE TO FURTHER WEAKENING OVER THE NEXT 24 HOURS AS THE SYSTEM APPROACHES HONG KONG. AFTER TAU 72, TY 09W WILL TURN SHARPLY EASTWARD AS THE STEERING INFLUENCE TRANSITIONS TO A LOW-LEVEL NEAR-EQUATORIAL RIDGE TO THE SOUTH AND ASSOCIATED VIGOROUS SOUTHWESTERLIES.

MODEL DISCUSSION: WITH THE EXCEPTION OF THE UKMET ENSEMBLE MEAN (UEMN), WHICH LOOPS THE SYSTEM SOUTH OF HONG KONG, NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT THROUGH TAU 36 WITH A 45 NM CROSS-TRACK SPREAD IN SOLUTIONS AT TAU 36. AFTER TAU 36, GUIDANCE DIVERGES WITH SIGNIFICANT DIFFERENCES IN THE DEGREE AND TIMING OF THE EASTWARD TURN. DUE TO THE LARGE DEGREE OF UNCERTAINTY, THERE IS MEDIUM OVERALL CONFIDENCE IN THE JTWC TRACK FORECAST THROUGH TAU 120. THE 311200Z ECMWF ENSEMBLE ALSO INDICATES SIGNIFICANT UNCERTAINTY IN THE TIMING OF THE EASTWARD TURN, POSSIBLY AS FAR WEST AS THE GULF OF TONKIN. THE 311800Z GFS ENSEMBLE SHOWS THE BULK OF THE SOLUTIONS TURNING THE SYSTEM OVER OR TO THE EAST OF HAINAN ISLAND. RELIABLE INTENSITY GUIDANCE IS IN FAIR AGREEMENT THROUGH TAU 120 LENDING MEDIUM CONFIDENCE TO THE JTWC INTENSITY FORECAST.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A CONSOLIDATING SYSTEM WITH DEEP CONVECTIVE BANDING WRAPPING INTO A DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC). A 312127Z SSMIS 91 GHZ COLOR COMPOSITE MICROWAVE IMAGE REVEALS IMPROVED CONVECTIVE STRUCTURE WITH SPIRAL BANDING WRAPPING TIGHTLY INTO A DEFINED MICROWAVE EYE FEATURE. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE SSMIS IMAGE. ANIMATED WATER VAPOR IMAGERY INDICATES IMPROVING RADIAL OUTFLOW, ESPECIALLY OVER THE NORTHERN SEMICIRCLE. THE INITIAL INTENSITY OF 70 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A BLEND OF THE AGENCY DVORAK ESTIMATES AND CIMSS ADT, AIDT ESTIMATES.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TYPHOON (TY) HAIKUI WILL TRACK WEST-NORTHWESTWARD ALONG THE SOUTHERN PERIPHERY OF THE STR THROUGH THE FORECAST PERIOD. TY 10W IS FORECAST TO INTENSIFY STEADILY THROUGH TAU 48 WITH A PEAK INTENSITY OF 105 KNOTS BY TAU 48 THEN IT WILL WEAKEN QUICKLY AS THE SYSTEM APPROACHES TAIWAN. TY 10W WILL CONTINUE TO WEAKEN SIGNIFICANTLY AS IT CROSSES THE MOUNTAINOUS TERRAIN OF TAIWAN WITH FURTHER WEAKENING AS IT TRACKS OVER SOUTHEAST CHINA.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE REMAINS IN FAIR AGREEMENT WITH A 115 NM CROSS-TRACK SPREAD IN SOLUTIONS AT TAU 72. WITH THE EXCEPTION OF GFS, WHICH INTERACTS WITH THE REMNANTS OF TYPHOON 09W, AND NAVGEM, THE NUMERICAL GUIDANCE REMAINS IN FAIR AGREEMENT THROUGH TAU 120. THUS, OVERALL CONFIDENCE IN THE JTWC TRACK FORECAST IS MEDIUM. THE JTWC INTENSITY FORECAST CONFIDENCE IS ALSO MEDIUM WITH SIGNIFICANT UNCERTAINTY IN THE PEAK INTENSITY OVER THE NEXT 60 HOURS. THE 311200Z COAMPS-TC ENSEMBLE INDICATES A 30 TO 40 PERCENT PROBABILITY OF RAPID INTENSIFICATION OCCURRING OVER THE NEXT 48 HOURS. ADDITIONALLY, RAPID INTENSIFICATION (RI) GUIDANCE HAS TRIGGERED SUGGESTING RI IS POSSIBLE WITHIN THE NEXT 48 HOURS.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS TROPICAL STORM (TS) KIROGI (11W) EXPERIENCING A MODERATE TO HIGHLY SHEARED ENVIRONMENT (20-25 KTS VWS) AND EXHIBITING A VERY DISORGANIZED OVERALL STRUCTURE. THE LOW LEVEL CIRCULATION CENTER (LLCC) IS FULLY EXPOSED TO THE SOUTHWEST OF THE STRUGGLING CONVECTIVE PLUME, WHICH SHOWS MUCH EVIDENCE OF SHEARING ALOFT AS THE CIRRUS FRAGMENTS PROPAGATE POLEWARD WITH THE NORTHWARD FLOW. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON A 010000Z HM9 PROXYVIS SATELLITE IMAGE. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON MULTIAGENCY DVORAK SUBJECTIVE INTENSITY ESTIMATES LISTED BELOW, AS WELL AS CIMSS ADT, AIDT, DPRINT OBJECTIVE INTENSITY ESTIMATES OF 49 KTS, 54 KTS, 48 KTS, RESPECTIVELY.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TS KIROGI IS FORECAST TO CONTINUE ON A NORTHWESTWARD TRACK THROUGH TAU 72, AND GRADUALLY SHIFT TO A WESTWARD TRACK THROUGH TAU 120. A GRADUAL WEAKENING IS EXPECTED THROUGH THE FORECAST PERIOD AS TS KIROGI CONTINUES TO EXPERIENCE A HIGHLY SHEARED ENVIRONMENT WITH THE ALREADY POORLY ORGANIZED STRUCTURE. PASSING NEARBY YAKUSHIMA ISLAND AROUND TAU 96 AT THE TROPICAL DEPRESSION INTENSITY LOWER THRESHOLD, THE SYSTEM IS ANTICIPATED TO ENTER THE EAST CHINA SEA AND LATER DISSIPATE PRIOR TO TAU 120.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE CONTINUES TO WEAKEN TS KIROGI THROUGH THE FORECAST PERIOD, AND TRENDS TO DISSIPATE THE SYSTEM EARLIER OVER MULTIPLE MODEL RUNS. MODELS REMAIN IN FAIR AGREEMENT THROUGH TAU 72 WITH A CROSS TRACK SPREAD OF 295NM. AFTER TAU 72, THE GFS DETERMINISTIC TRACK CURLS COUNTERCLOCKWISE TO A RECIPROCAL HEADING TO THE NORTHEAST AT TAU 120. THE OPPOSING OUTLIER, BEING NAVGEM, TRACKS THE SYSTEM AROUND THE STR TO THE NORTH RESULTING IN A NORTHEASTWARD TRACK THROUGH TAU 120. THE BULK OF NUMERICAL GUIDANCE, TO INCLUDE THE MAJORITY OF ENSEMBLE MEMBERS, TRACK THE SYSTEM WESTWARD TO DISSIPATION IN THE EAST CHINA SEA.

Last Updated - 08/29/23 Valid - 09/06/23 - 09/19/23 The atmospheric response to the ongoing El Nino conditions across the central and eastern Pacific remains the primary driver of global tropical convective anomalies. A downwelling oceanic Kelvin wave is currently bringing a new round of warmer upper-ocean water across the central Pacific, which should reinforce the ongoing ENSO event, and ocean temperatures over the West Pacific Warm Pool have begun to decrease, which may further weaken the Walker circulation with time, resulting in a more canonical atmospheric response. Following a period of incoherence, the MJO has recently become more active, with the CPC upper-level velocity potential index reflecting an eastward propagating signal across the Western Hemisphere. Although the signal is less substantial on the RMM-based MJO index, dynamical model MJO index forecasts have become increasingly confident in continued evolution of the intraseasonal signal, with a robust amplitude MJO footprint over the Maritime Continent during Week-2, and many ensemble members propagating the signal to the West Pacific in Week-3. Based on these forecasts, the MJO is favored to play an increasing role in the global tropical convective pattern over the next few weeks, with its impacts somewhat destructively interfering with the ENSO base state during Week-2, with constructive interference increasing during Week-3. Several tropical cyclones formed during the past week. Tropical Storm Harold formed over the Gulf of Mexico on 22 August, just prior to making landfall over southern Texas. The system brought widespread heavy rainfall to southern Texas and the lower Rio Grande Valley. Hurricane Idalia formed over the far western Caribbean on 27 August, and is currently moving northward over the eastern Gulf of Mexico. Forecasts from the National Hurricane Center indicate a potential for rapid intensification over the next day, with devastating impacts possible along Apalachee Bay, and more widespread wind and rain impacts across the far southeastern CONUS. Tropical Depression Eleven also formed over the central Atlantic, with little impacts anticipated over the next few days. Across the East Pacific, Tropical Storm Irwin formed well southwest of Mexico, and is forecast to gradually dissipate while moving westward over cooler waters. Over the West Pacific, Typhoon Saola has meandered near Luzon for several days, and is forecast to move into the South China Sea during Week-1, while Tropical Storm Haikui is favored to strengthen to typhoon intensity while tracking gradually west-northwestward away from Guam and towards the East China Sea. During Week-2, the enhanced convective phase of the MJO propagating from the Maritime Continent to the West Pacific is typically associated with enhanced tropical cyclone activity over the South China Sea and portions of the Northwest Pacific. This activity is supported by dynamical model forecasts. Therefore, there is high confidence for tropical cyclone formations over the South China Sea, with moderate confidence extending eastward to the Northwest Pacific northwest of Luzon. A broader region exceeding 20-percent chances for formation exists across much of the Northwest Pacific near and west of Guam. During Week-3, a broader region of favorability is highlighted, extending further southeast across the West Pacific basin. Across the East Pacific, the forecasted MJO activity is generally unfavorable for development, but due to ongoing El Nino conditions and some dynamical model support, a region of 20-percent chances for development is included well southwest of Mexico. Across the Atlantic basin, both the El Nino and MJO states would favor a break in activity; however, due to very warm SSTs across much of the basin, as well as peak climatology occurring during the outlook period, a broad area of 20-percent chances for formation was included across the MDR, with favorability extending into higher latitudes based on the ocean temperatures. During Week-3, confidence for development increases somewhat across both the East Pacific and Atlantic basins, although dynamical models show a relatively quiet Caribbean and Gulf of Mexico. Forecasts for above- and below-normal precipitation are based on composites of historical El Nino events, MJO activity over the Maritime Continent and West Pacific, and a skill weighted consensus of dynamical model guidance. A highly amplified ridge over South America is favored to shift, bringing a potential for wet conditions across southern Brazil, northwestern Argentina, Uruguay, and Paraguay, while persistent ridging continues to favor above-normal temperatures for the central U.S. Subsidence south of enhanced precipitation associated with El Nino conditions may bring drier conditions to American Samoa. For hazardous weather conditions in your area during the coming two-week period, please refer to your local NWS office, the Medium Range Hazards Forecast produced by the Weather Prediction Center, and the CPC Week-2 Hazards Outlook. Forecasts made over Africa are made in coordination with the International Desk at CPC.