RAINMUMBAI Index Desk

NCDEX Mumbai rainfall futures · Cumulative Deviation Rainfall
NCDEX spot As on Sunday, August 30, 2026 09:30 AM · page generated 30 Aug 2026 16:30 IST

What this index is. RAINMUMBAI settles on how far Mumbai's monsoon rain runs above or below normal. The index opens each 1 June at 2,206.7 mm — the 30-year normal for the whole season — then each day adds the actual rainfall at the Colaba and Santacruz observatories and subtracts the normal for that date. Rising means wetter than normal; falling means drier. One millimetre is worth Rs 50 per lot, so the whole page can be read in rupees as well as rainfall.

The four figures below are today's position: where the index actually is, how far that is from the season's starting point, how much the two forecast models disagree about the next two weeks, and how this season compares with recent ones.

Official spot

2,368mm

30 Aug · Rs 118,422/lot

vs anchor

+162mm

excess

Model spread

99mm

at 13 Sep · Rs 4,940/lot

Season rank

20th pct

of 5 seasons on this date

Season index and forward projection

The solid line is what has already happened this season. The two dashed lines are where each model expects the index to go next — they start from today's value, so any gap between them is pure forecast disagreement.

NCDEX official spot VM-AIFS projection VM-IFS projection 5-season median 10th–90th percentile

The grey band shows where the index sat on each date across 2021–2025, so a line inside the band is an ordinary season and one outside it is unusual. VM-AIFS and VM-IFS are VayuMet projections built on ECMWF AIFS and IFS fields at 0.25°, read at 19.00N 72.75E, aligned to the 03Z–03Z settlement window and bias-corrected against the settlement series.

Where the models disagree

Day by day, how much rain each model expects, the normal for that date, and where each one puts the index. The last column is the gap between them — small means the two agree, large means the forecast is genuinely uncertain.

Date	Lead	VM-AIFS mm	VM-IFS mm	LPA	VM-AIFS CDR	VM-IFS CDR	Gap
31 Aug	2	3.3	9.8	18.1	2,354	2,360	-6
01 Sep	3	4.2	7.8	16.6	2,341	2,351	-10
02 Sep	4	5.8	16.8	18.4	2,329	2,350	-21
03 Sep	5	6.7	11.2	17.4	2,318	2,344	-25
04 Sep	6	6.2	7.9	17.7	2,307	2,334	-27
05 Sep	7	7.2	9.3	12.9	2,301	2,330	-29
06 Sep	8	5.0	10.5	9.4	2,296	2,331	-35
07 Sep	9	3.3	14.6	7.3	2,292	2,338	-46
08 Sep	10	2.7	12.6	8.4	2,287	2,343	-56
09 Sep	11	2.6	10.2	9.8	2,280	2,343	-64
10 Sep	12	2.6	8.2	13.6	2,269	2,338	-69
11 Sep	13	4.1	10.8	11.3	2,261	2,337	-76
12 Sep	14	6.1	11.6	8.9	2,259	2,340	-81
13 Sep	14	2.6	11.2	11.1	2,247	2,346	-99

Where the two sources diverge, that gap is the honest uncertainty — and it is wider than either model's own error statistics imply. Both under-forecast heavy rain substantially, so treat any active spell in these trajectories as a lower bound.

Verification — out of sample

How each model has actually performed once the real rainfall was published. Bias is the average miss and its sign shows the direction — positive means too wet. MAE is the typical miss ignoring direction; lower is better on both.

Model	Lead	n	Bias	MAE	RMSE
AIFS	D+1	3	+1.39	2.73	2.82
AIFS	D+2	3	+1.41	2.59	2.70
AIFS	D+3	3	+1.38	2.72	2.80
AIFS	D+4	3	+1.66	3.02	3.15
AIFS	D+5	3	+1.77	2.96	3.08
IFS	D+1	3	+6.33	6.33	6.88
IFS	D+2	3	+5.56	5.56	6.03
IFS	D+3	3	+6.06	6.06	6.69
IFS	D+4	3	+6.77	6.77	7.16
IFS	D+5	3	+5.58	5.58	5.86

3 settlement day(s) scored against the official spot. Below about 30 days this is provisional, not a track record.

Traded curve

The last traded price of each monthly contract, and how far that sits from today's index. A large gap is the market pricing in rain, or the lack of it, over the days still to come.

Contract	Last	vs spot	As of
2026-06-29(Jun Fut)	2,096.00	-272.4	30 Jun
2026-07-30(Jul Fut)	2,635.00	+266.6	31 Jul
2026-08-28(Aug Fut)	2,376.00	+7.6	28 Aug
2026-09-29(Sep Fut)	2,140.00	-228.4	28 Aug

Futures converge to the spot at expiry, so a wide basis late in a contract month is a view on the days that remain.